Storing directory metadata in a dispersed storage network

ABSTRACT

A method begins by a processing module dispersed storage error encoding data to produce encoded data slices and updating directory metadata regarding storing the data in a dispersed storage network (DSN) memory to produce updated directory metadata. The method continues with the processing module dispersed storage error encoding the updated directory metadata to produce encoded directory metadata slices and transmitting one or more data slice write requests to the DSN that each include a first transaction number. The method continues with the processing module transmitting one or more directory metadata write requests to the DSN memory, wherein the one or more directory metadata write requests includes a second transaction number, and when a favorable write response condition exists, transmitting a commit request to the DSN memory to commit storage of at least one of: the encoded data slices and the encoded directory metadata slices.

CROSS REFERENCE TO RELATED PATENTS

The present U.S. Utility patent application claims priority pursuant to35 U.S.C. §120 as a continuation of U.S. Utility application Ser. No.13/308,724, entitled “Storing directory metadata in a dispersed storagenetwork”, filed Dec. 1, 2011, now U.S. Pat. No. 8,832,493, issued onSep. 9, 2014, which claims priority pursuant to 35 U.S.C. §119(e) toU.S. Provisional Application No. 61/426,237, entitled “Dispersed StorageNetwork File System”, filed Dec. 22, 2010, both of which are herebyincorporated herein by reference in their entirety and made part of thepresent U.S. Utility patent application for all purposes.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable

INCORPORATION-BY-REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISC

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BACKGROUND OF THE INVENTION

1. Technical Field of the Invention

This invention relates generally to computing systems and moreparticularly to data storage solutions within such computing systems.

2. Description of Related Art

Computers are known to communicate, process, and store data. Suchcomputers range from wireless smart phones to data centers that supportmillions of web searches, stock trades, or on-line purchases every day.In general, a computing system generates data and/or manipulates datafrom one form into another. For instance, an image sensor of thecomputing system generates raw picture data and, using an imagecompression program (e.g., JPEG, MPEG, etc.), the computing systemmanipulates the raw picture data into a standardized compressed image.

With continued advances in processing speed and communication speed,computers are capable of processing real time multimedia data forapplications ranging from simple voice communications to streaming highdefinition video. As such, general-purpose information appliances arereplacing purpose-built communications devices (e.g., a telephone). Forexample, smart phones can support telephony communications but they arealso capable of text messaging and accessing the internet to performfunctions including email, web browsing, remote applications access, andmedia communications (e.g., telephony voice, image transfer, musicfiles, video files, real time video streaming, etc.).

Each type of computer is constructed and operates in accordance with oneor more communication, processing, and storage standards. As a result ofstandardization and with advances in technology, more and moreinformation content is being converted into digital formats. Forexample, more digital cameras are now being sold than film cameras, thusproducing more digital pictures. As another example, web-basedprogramming is becoming an alternative to over the air televisionbroadcasts and/or cable broadcasts. As further examples, papers, books,video entertainment, home video, etc. are now being stored digitally,which increases the demand on the storage function of computers.

A typical computer storage system includes one or more memory devicesaligned with the needs of the various operational aspects of thecomputer's processing and communication functions. Generally, theimmediacy of access dictates what type of memory device is used. Forexample, random access memory (RAM) memory can be accessed in any randomorder with a constant response time, thus it is typically used for cachememory and main memory. By contrast, memory device technologies thatrequire physical movement such as magnetic disks, tapes, and opticaldiscs, have a variable response time as the physical movement can takelonger than the data transfer, thus they are typically used forsecondary memory (e.g., hard drive, backup memory, etc.).

A computer's storage system will be compliant with one or more computerstorage standards that include, but are not limited to, network filesystem (NFS), flash file system (FFS), disk file system (DFS), smallcomputer system interface (SCSI), internet small computer systeminterface (iSCSI), file transfer protocol (FTP), and web-baseddistributed authoring and versioning (WebDAV). These standards specifythe data storage format (e.g., files, data objects, data blocks,directories, etc.) and interfacing between the computer's processingfunction and its storage system, which is a primary function of thecomputer's memory controller.

Despite the standardization of the computer and its storage system,memory devices fail; especially commercial grade memory devices thatutilize technologies incorporating physical movement (e.g., a discdrive). For example, it is fairly common for a disc drive to routinelysuffer from bit level corruption and to completely fail after threeyears of use. One solution is to utilize a higher-grade disc drive,which adds significant cost to a computer.

Another solution is to utilize multiple levels of redundant disc drivesto replicate the data into two or more copies. One such redundant driveapproach is called redundant array of independent discs (RAID). In aRAID device, a RAID controller adds parity data to the original databefore storing it across the array. The parity data is calculated fromthe original data such that the failure of a disc will not result in theloss of the original data. For example, RAID 5 uses three discs toprotect data from the failure of a single disc. The parity data, andassociated redundancy overhead data, reduces the storage capacity ofthree independent discs by one third (e.g., n−1=capacity). RAID 6 canrecover from a loss of two discs and requires a minimum of four discswith a storage capacity of n−2.

While RAID addresses the memory device failure issue, it is not withoutits own failure issues that affect its effectiveness, efficiency andsecurity. For instance, as more discs are added to the array, theprobability of a disc failure increases, which increases the demand formaintenance. For example, when a disc fails, it needs to be manuallyreplaced before another disc fails and the data stored in the RAIDdevice is lost. To reduce the risk of data loss, data on a RAID deviceis typically copied on to one or more other RAID devices. While thisaddresses the loss of data issue, it raises a security issue sincemultiple copies of data are available, which increases the chances ofunauthorized access. Further, as the amount of data being stored grows,the overhead of RAID devices becomes a non-trivial efficiency issue.

Another solution is to utilize dispersed storage wherein data issegmented to produce a plurality of data segments wherein each datasegment of the plurality of data segments is dispersed storage errorencoded to produce a set of encoded data slices of a plurality of setsof encoded data slices that are stored within a dispersed storagenetwork memory. A plurality of sets of slice names are generated thatcorrespond to the plurality of sets of encoded data slices, wherein eachslice name provides a virtual dispersed storage network memory addressto access and associated encoded data slice within the dispersed storagenetwork memory. The number of data segments of the plurality of datasegments depends on a segmentation scheme and the size of the data. Adata size indicator may be appended to a first data segment of theplurality of data segments prior to the dispersed storage error encodingof the first data segment. Retrieving the data from the dispersedstorage network requires a first operation to retrieve a set of encodeddata slices associated with the first data segment to reproduce thefirst data segment and the appended data size indicator. A secondoperation may retrieve subsequent data segments of the plurality of datasegments based on the data size indicator (e.g., enabling generating anappropriate number of sets of slice names corresponding to thesubsequent data segments). Some data retrieval scenarios may require anaccess latency time associated with just one operation.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

FIG. 1 is a schematic block diagram of an embodiment of a computingsystem in accordance with the invention;

FIG. 2 is a schematic block diagram of an embodiment of a computing corein accordance with the invention;

FIG. 3 is a schematic block diagram of an embodiment of a distributedstorage processing unit in accordance with the invention;

FIG. 4 is a schematic block diagram of an embodiment of a grid module inaccordance with the invention;

FIG. 5 is a diagram of an example embodiment of error coded data slicecreation in accordance with the invention;

FIG. 6 is a flowchart illustrating an example of updating a directory inaccordance with the invention;

FIG. 7 is a flowchart illustrating another example of updating adirectory in accordance with the invention;

FIG. 8 is a flowchart illustrating an example of synchronizing directoryinformation in accordance with the invention;

FIG. 9 is a flowchart illustrating another example of synchronizingdirectory information in accordance with the invention;

FIG. 10A is a diagram illustrating an example of a snapshot file and adirectory file relationship in accordance with the invention;

FIG. 10B is a diagram illustrating another example of a snapshot fileand a directory file relationship in accordance with the invention;

FIG. 10C is a diagram illustrating another example of a snapshot fileand a directory file relationship in accordance with the invention;

FIG. 10D is a diagram illustrating another example of a snapshot fileand a directory file relationship in accordance with the invention;

FIG. 10E is a diagram illustrating another example of a snapshot fileand a directory file relationship in accordance with the invention;

FIG. 10F is a diagram illustrating another example of a snapshot fileand a directory file relationship in accordance with the invention;

FIG. 10G is a diagram illustrating another example of a snapshot fileand a directory file relationship in accordance with the invention;

FIG. 10H is a diagram illustrating another example of a snapshot fileand a directory file relationship in accordance with the invention;

FIG. 11A is a flowchart illustrating an example of adding a snapshot inaccordance with the invention;

FIG. 11B is a flowchart illustrating an example of deleting a snapshotin accordance with the invention;

FIG. 12A is a flowchart illustrating another example of updating adirectory in accordance with the invention;

FIG. 12B is a flowchart illustrating another example of updating adirectory in accordance with the invention;

FIG. 13 is a flowchart illustrating an example of storing data inaccordance with the invention;

FIG. 14A is a flowchart illustrating another example of storing data inaccordance with the invention;

FIG. 14B is a block diagram of a storing module in accordance with theinvention;

FIG. 15 is a diagram illustrating an example of a segmentationallocation table in accordance with the invention;

FIG. 16A is a diagram illustrating an example of a slice name format inaccordance with the invention;

FIG. 16B is a diagram illustrating an example of data segmentation inaccordance with the invention;

FIG. 16C is a diagram illustrating another example of data segmentationin accordance with the invention;

FIG. 17A is a flowchart illustrating an example of segmenting data inaccordance with the invention;

FIG. 17B is a block diagram of a segmenting module in accordance withthe invention;

FIG. 18 is a diagram illustrating an example of a directory file formatin accordance with the invention;

FIG. 19 is a flowchart illustrating another example of updating adirectory in accordance with the invention;

FIG. 20A is a diagram illustrating another example of a slice nameformat in accordance with the invention;

FIG. 20B is a diagram illustrating an example of data segmentation inaccordance with the invention;

FIG. 20C is a diagram illustrating another example of data segmentationin accordance with the invention;

FIG. 21 is a flowchart illustrating another example of segmenting datain accordance with the invention;

FIG. 22A is a flowchart illustrating an example of retrieving data inaccordance with the invention;

FIG. 22B is a block diagram of a reproduce data module in accordancewith the invention;

FIG. 22C is a flowchart illustrating another example of retrieving datain accordance with the invention;

FIG. 22D is a block diagram of another reproduce data module inaccordance with the invention; and

FIG. 23 is a flowchart illustrating another example of storing data inaccordance with the invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a schematic block diagram of a computing system 10 thatincludes one or more of a first type of user devices 12, one or more ofa second type of user devices 14, at least one distributed storage (DS)processing unit 16, at least one DS managing unit 18, at least onestorage integrity processing unit 20, and a distributed storage network(DSN) memory 22 coupled via a network 24. The network 24 may include oneor more wireless and/or wire lined communication systems; one or moreprivate intranet systems and/or public internet systems; and/or one ormore local area networks (LAN) and/or wide area networks (WAN).

The DSN memory 22 includes a plurality of distributed storage (DS) units36 for storing data of the system. Each of the DS units 36 includes aprocessing module and memory and may be located at a geographicallydifferent site than the other DS units (e.g., one in Chicago, one inMilwaukee, etc.).

Each of the user devices 12-14, the DS processing unit 16, the DSmanaging unit 18, and the storage integrity processing unit 20 may be aportable computing device (e.g., a social networking device, a gamingdevice, a cell phone, a smart phone, a personal digital assistant, adigital music player, a digital video player, a laptop computer, ahandheld computer, a video game controller, and/or any other portabledevice that includes a computing core) and/or a fixed computing device(e.g., a personal computer, a computer server, a cable set-top box, asatellite receiver, a television set, a printer, a fax machine, homeentertainment equipment, a video game console, and/or any type of homeor office computing equipment). Such a portable or fixed computingdevice includes a computing core 26 and one or more interfaces 30, 32,and/or 33. An embodiment of the computing core 26 will be described withreference to FIG. 2.

With respect to the interfaces, each of the interfaces 30, 32, and 33includes software and/or hardware to support one or more communicationlinks via the network 24 indirectly and/or directly. For example,interfaces 30 support a communication link (wired, wireless, direct, viaa LAN, via the network 24, etc.) between the first type of user device14 and the DS processing unit 16. As another example, DSN interface 32supports a plurality of communication links via the network 24 betweenthe DSN memory 22 and the DS processing unit 16, the first type of userdevice 12, and/or the storage integrity processing unit 20. As yetanother example, interface 33 supports a communication link between theDS managing unit 18 and any one of the other devices and/or units 12,14, 16, 20, and/or 22 via the network 24.

In general and with respect to data storage, the system 10 supportsthree primary functions: distributed network data storage management,distributed data storage and retrieval, and data storage integrityverification. In accordance with these three primary functions, data canbe distributedly stored in a plurality of physically different locationsand subsequently retrieved in a reliable and secure manner regardless offailures of individual storage devices, failures of network equipment,the duration of storage, the amount of data being stored, attempts athacking the data, etc.

The DS managing unit 18 performs distributed network data storagemanagement functions, which include establishing distributed datastorage parameters, performing network operations, performing networkadministration, and/or performing network maintenance. The DS managingunit 18 establishes the distributed data storage parameters (e.g.,allocation of virtual DSN memory space, distributed storage parameters,security parameters, billing information, user profile information,etc.) for one or more of the user devices 12-14 (e.g., established forindividual devices, established for a user group of devices, establishedfor public access by the user devices, etc.). For example, the DSmanaging unit 18 coordinates the creation of a vault (e.g., a virtualmemory block) within the DSN memory 22 for a user device (for a group ofdevices, or for public access). The DS managing unit 18 also determinesthe distributed data storage parameters for the vault. In particular,the DS managing unit 18 determines a number of slices (e.g., the numberthat a data segment of a data file and/or data block is partitioned intofor distributed storage) and a read threshold value (e.g., the minimumnumber of slices required to reconstruct the data segment).

As another example, the DS managing module 18 creates and stores,locally or within the DSN memory 22, user profile information. The userprofile information includes one or more of authentication information,permissions, and/or the security parameters. The security parameters mayinclude one or more of encryption/decryption scheme, one or moreencryption keys, key generation scheme, and data encoding/decodingscheme.

As yet another example, the DS managing unit 18 creates billinginformation for a particular user, user group, vault access, publicvault access, etc. For instance, the DS managing unit 18 tracks thenumber of times user accesses a private vault and/or public vaults,which can be used to generate a per-access bill. In another instance,the DS managing unit 18 tracks the amount of data stored and/orretrieved by a user device and/or a user group, which can be used togenerate a per-data-amount bill.

The DS managing unit 18 also performs network operations, networkadministration, and/or network maintenance. As at least part ofperforming the network operations and/or administration, the DS managingunit 18 monitors performance of the devices and/or units of the system10 for potential failures, determines the devices' and/or unitsactivation status, determines the devices' and/or units' loading, andany other system level operation that affects the performance level ofthe system 10. For example, the DS managing unit 18 receives andaggregates network management alarms, alerts, errors, statusinformation, performance information, and messages from the devices12-14 and/or the units 16, 20, 22. For example, the DS managing unit 18receives a simple network management protocol (SNMP) message regardingthe status of the DS processing unit 16.

The DS managing unit 18 performs the network maintenance by identifyingequipment within the system 10 that needs replacing, upgrading,repairing, and/or expanding. For example, the DS managing unit 18determines that the DSN memory 22 needs more DS units 36 or that one ormore of the DS units 36 needs updating.

The second primary function (i.e., distributed data storage andretrieval) begins and ends with a user device 12-14. For instance, if asecond type of user device 14 has a data file 38 and/or data block 40 tostore in the DSN memory 22, it sends the data file 38 and/or data block40 to the DS processing unit 16 via its interface 30. As will bedescribed in greater detail with reference to FIG. 2, the interface 30functions to mimic a conventional operating system (OS) file systeminterface (e.g., network file system (NFS), flash file system (FFS),disk file system (DFS), file transfer protocol (FTP), web-baseddistributed authoring and versioning (WebDAV), etc.) and/or a blockmemory interface (e.g., small computer system interface (SCSI), internetsmall computer system interface (iSCSI), etc.). In addition, theinterface 30 may attach a user identification code (ID) to the data file38 and/or data block 40.

The DS processing unit 16 receives the data file 38 and/or data block 40via its interface 30 and performs a distributed storage (DS) process 34thereon (e.g., an error coding dispersal storage function). The DSprocessing 34 begins by partitioning the data file 38 and/or data block40 into one or more data segments, which is represented as Y datasegments. For example, the DS processing 34 may partition the data file38 and/or data block 40 into a fixed byte size segment (e.g., 2¹ to2^(n) bytes, where n=>2) or a variable byte size (e.g., change byte sizefrom segment to segment, or from groups of segments to groups ofsegments, etc.).

For each of the Y data segments, the DS processing 34 error encodes(e.g., forward error correction (FEC), information dispersal algorithm,or error correction coding) and slices (or slices then error encodes)the data segment into a plurality of error coded (EC) data slices 42-48,which is represented as X slices per data segment. The number of slices(X) per segment, which corresponds to a number of pillars n, is set inaccordance with the distributed data storage parameters and the errorcoding scheme. For example, if a Reed-Solomon (or other FEC scheme) isused in an n/k system, then a data segment is divided into n slices,where k number of slices is needed to reconstruct the original data(i.e., k is the threshold). As a few specific examples, the n/k factormay be 5/3; 6/4; 8/6; 8/5; 16/10.

For each EC slice 42-48, the DS processing unit 16 creates a uniqueslice name and appends it to the corresponding slice EC 42-48. The slicename includes universal DSN memory addressing routing information (e.g.,virtual memory addresses in the DSN memory 22) and user-specificinformation (e.g., user ID, file name, data block identifier, etc.).

The DS processing unit 16 transmits the plurality of EC slices 42-48 toa plurality of DS units 36 of the DSN memory 22 via the DSN interface 32and the network 24. The DSN interface 32 formats each of the slices fortransmission via the network 24. For example, the DSN interface 32 mayutilize an internet protocol (e.g., TCP/IP, etc.) to packetize the ECslices 42-48 for transmission via the network 24.

The number of DS units 36 receiving the EC slices 42-48 is dependent onthe distributed data storage parameters established by the DS managingunit 18. For example, the DS managing unit 18 may indicate that eachslice is to be stored in a different DS unit 36. As another example, theDS managing unit 18 may indicate that like slice numbers of differentdata segments are to be stored in the same DS unit 36. For example, thefirst slice of each of the data segments is to be stored in a first DSunit 36, the second slice of each of the data segments is to be storedin a second DS unit 36, etc. In this manner, the data is encoded anddistributedly stored at physically diverse locations to improve datastorage integrity and security.

Each DS unit 36 that receives an EC slice 42-48 for storage translatesthe virtual DSN memory address of the slice into a local physicaladdress for storage. Accordingly, each DS unit 36 maintains a virtual tophysical memory mapping to assist in the storage and retrieval of data.

The first type of user device 12 performs a similar function to storedata in the DSN memory 22 with the exception that it includes the DSprocessing. As such, the device 12 encodes and slices the data fileand/or data block it has to store. The device then transmits the slices11 to the DSN memory via its DSN interface 32 and the network 24.

For a second type of user device 14 to retrieve a data file or datablock from memory, it issues a read command via its interface 30 to theDS processing unit 16. The DS processing unit 16 performs the DSprocessing 34 to identify the DS units 36 storing the slices of the datafile and/or data block based on the read command. The DS processing unit16 may also communicate with the DS managing unit 18 to verify that theuser device 14 is authorized to access the requested data.

Assuming that the user device is authorized to access the requesteddata, the DS processing unit 16 issues slice read commands to at least athreshold number of the DS units 36 storing the requested data (e.g., toat least 10 DS units for a 16/10 error coding scheme). Each of the DSunits 36 receiving the slice read command, verifies the command,accesses its virtual to physical memory mapping, retrieves the requestedslice, or slices, and transmits it to the DS processing unit 16.

Once the DS processing unit 16 has received a read threshold number ofslices for a data segment, it performs an error decoding function andde-slicing to reconstruct the data segment. When Y number of datasegments has been reconstructed, the DS processing unit 16 provides thedata file 38 and/or data block 40 to the user device 14. Note that thefirst type of user device 12 performs a similar process to retrieve adata file and/or data block.

The storage integrity processing unit 20 performs the third primaryfunction of data storage integrity verification. In general, the storageintegrity processing unit 20 periodically retrieves slices 45, and/orslice names, of a data file or data block of a user device to verifythat one or more slices have not been corrupted or lost (e.g., the DSunit failed). The retrieval process mimics the read process previouslydescribed.

If the storage integrity processing unit 20 determines that one or moreslices is corrupted or lost, it rebuilds the corrupted or lost slice(s)in accordance with the error coding scheme. The storage integrityprocessing unit 20 stores the rebuild slice, or slices, in theappropriate DS unit(s) 36 in a manner that mimics the write processpreviously described.

FIG. 2 is a schematic block diagram of an embodiment of a computing core26 that includes a processing module 50, a memory controller 52, mainmemory 54, a video graphics processing unit 55, an input/output (IO)controller 56, a peripheral component interconnect (PCI) interface 58,an IO interface 60, at least one IO device interface module 62, a readonly memory (ROM) basic input output system (BIOS) 64, and one or morememory interface modules. The memory interface module(s) includes one ormore of a universal serial bus (USB) interface module 66, a host busadapter (HBA) interface module 68, a network interface module 70, aflash interface module 72, a hard drive interface module 74, and a DSNinterface module 76. Note the DSN interface module 76 and/or the networkinterface module 70 may function as the interface 30 of the user device14 of FIG. 1. Further note that the IO device interface module 62 and/orthe memory interface modules may be collectively or individuallyreferred to as IO ports.

FIG. 3 is a schematic block diagram of an embodiment of a dispersedstorage (DS) processing module 34 of user device 12 and/or of the DSprocessing unit 16. The DS processing module 34 includes a gatewaymodule 78, an access module 80, a grid module 82, and a storage module84. The DS processing module 34 may also include an interface 30 and theDSnet interface 32 or the interfaces 68 and/or 70 may be part of userdevice 12 or of the DS processing unit 16. The DS processing module 34may further include a bypass/feedback path between the storage module 84to the gateway module 78. Note that the modules 78-84 of the DSprocessing module 34 may be in a single unit or distributed acrossmultiple units.

In an example of storing data, the gateway module 78 receives anincoming data object that includes a user ID field 86, an object namefield 88, and the data object field 40 and may also receivecorresponding information that includes a process identifier (e.g., aninternal process/application ID), metadata, a file system directory, ablock number, a transaction message, a user device identity (ID), a dataobject identifier, a source name, and/or user information. The gatewaymodule 78 authenticates the user associated with the data object byverifying the user ID 86 with the managing unit 18 and/or anotherauthenticating unit.

When the user is authenticated, the gateway module 78 obtains userinformation from the management unit 18, the user device, and/or theother authenticating unit. The user information includes a vaultidentifier, operational parameters, and user attributes (e.g., userdata, billing information, etc.). A vault identifier identifies a vault,which is a virtual memory space that maps to a set of DS storage units36. For example, vault 1 (i.e., user 1's DSN memory space) includeseight DS storage units (X=8 wide) and vault 2 (i.e., user 2's DSN memoryspace) includes sixteen DS storage units (X=16 wide). The operationalparameters may include an error coding algorithm, the width n (number ofpillars X or slices per segment for this vault), a read threshold T, awrite threshold, an encryption algorithm, a slicing parameter, acompression algorithm, an integrity check method, caching settings,parallelism settings, and/or other parameters that may be used to accessthe DSN memory layer.

The gateway module 78 uses the user information to assign a source name35 to the data. For instance, the gateway module 78 determines thesource name 35 of the data object 40 based on the vault identifier andthe data object. For example, the source name may contain a fileidentifier (ID), a vault generation number, a reserved field, and avault identifier (ID). As another example, the gateway module 78 maygenerate the file ID based on a hash function of the data object 40.Note that the gateway module 78 may also perform message conversion,protocol conversion, electrical conversion, optical conversion, accesscontrol, user identification, user information retrieval, trafficmonitoring, statistics generation, configuration, management, and/orsource name determination.

The access module 80 receives the data object 40 and creates a series ofdata segments 1 through Y 90-92 in accordance with a data storageprotocol (e.g., file storage system, a block storage system, and/or anaggregated block storage system). The number of segments Y may be chosenor randomly assigned based on a selected segment size and the size ofthe data object. For example, if the number of segments is chosen to bea fixed number, then the size of the segments varies as a function ofthe size of the data object. For instance, if the data object is animage file of 4,194,304 eight bit bytes (e.g., 33,554,432 bits) and thenumber of segments Y=131,072, then each segment is 256 bits or 32 bytes.As another example, if segment sized is fixed, then the number ofsegments Y varies based on the size of data object. For instance, if thedata object is an image file of 4,194,304 bytes and the fixed size ofeach segment is 4,096 bytes, then the number of segments Y=1,024. Notethat each segment is associated with the same source name.

The grid module 82 receives the data segments and may manipulate (e.g.,compression, encryption, cyclic redundancy check (CRC), etc.) each ofthe data segments before performing an error coding function of theerror coding dispersal storage function to produce a pre-manipulateddata segment. After manipulating a data segment, if applicable, the gridmodule 82 error encodes (e.g., Reed-Solomon, Convolution encoding,Trellis encoding, etc.) the data segment or manipulated data segmentinto X error coded data slices 42-44.

The value X, or the number of pillars (e.g., X=16), is chosen as aparameter of the error coding dispersal storage function. Otherparameters of the error coding dispersal function include a readthreshold T, a write threshold W, etc. The read threshold (e.g., T=10,when X=16) corresponds to the minimum number of error-free error codeddata slices required to reconstruct the data segment. In other words,the DS processing module 34 can compensate for X-T (e.g., 16−10=6)missing error coded data slices per data segment. The write threshold Wcorresponds to a minimum number of DS storage units that acknowledgeproper storage of their respective data slices before the DS processingmodule indicates proper storage of the encoded data segment. Note thatthe write threshold is greater than or equal to the read threshold for agiven number of pillars (X).

For each data slice of a data segment, the grid module 82 generates aunique slice name 37 and attaches it thereto. The slice name 37 includesa universal routing information field and a vault specific field and maybe 48 bytes (e.g., 24 bytes for each of the universal routinginformation field and the vault specific field). As illustrated, theuniversal routing information field includes a slice index, a vault ID,a vault generation, and a reserved field. The slice index is based onthe pillar number and the vault ID and, as such, is unique for eachpillar (e.g., slices of the same pillar for the same vault for anysegment will share the same slice index). The vault specific fieldincludes a data name, which includes a file ID and a segment number(e.g., a sequential numbering of data segments 1-Y of a simple dataobject or a data block number).

Prior to outputting the error coded data slices of a data segment, thegrid module may perform post-slice manipulation on the slices. Ifenabled, the manipulation includes slice level compression, encryption,CRC, addressing, tagging, and/or other manipulation to improve theeffectiveness of the computing system.

When the error coded data slices of a data segment are ready to beoutputted, the grid module 82 determines which of the DS storage units36 will store the EC data slices based on a dispersed storage memorymapping associated with the user's vault and/or DS storage unitattributes. The DS storage unit attributes may include availability,self-selection, performance history, link speed, link latency,ownership, available DSN memory, domain, cost, a prioritization scheme,a centralized selection message from another source, a lookup table,data ownership, and/or any other factor to optimize the operation of thecomputing system. Note that the number of DS storage units 36 is equalto or greater than the number of pillars (e.g., X) so that no more thanone error coded data slice of the same data segment is stored on thesame DS storage unit 36. Further note that EC data slices of the samepillar number but of different segments (e.g., EC data slice 1 of datasegment 1 and EC data slice 1 of data segment 2) may be stored on thesame or different DS storage units 36.

The storage module 84 performs an integrity check on the outboundencoded data slices and, when successful, identifies a plurality of DSstorage units based on information provided by the grid module 82. Thestorage module 84 then outputs the encoded data slices 1 through X ofeach segment 1 through Y to the DS storage units 36. Each of the DSstorage units 36 stores its EC data slice(s) and maintains a localvirtual DSN address to physical location table to convert the virtualDSN address of the EC data slice(s) into physical storage addresses.

In an example of a read operation, the user device 12 and/or 14 sends aread request to the DS processing unit 16, which authenticates therequest. When the request is authentic, the DS processing unit 16 sendsa read message to each of the DS storage units 36 storing slices of thedata object being read. The slices are received via the DSnet interface32 and processed by the storage module 84, which performs a parity checkand provides the slices to the grid module 82 when the parity check wassuccessful. The grid module 82 decodes the slices in accordance with theerror coding dispersal storage function to reconstruct the data segment.The access module 80 reconstructs the data object from the data segmentsand the gateway module 78 formats the data object for transmission tothe user device.

FIG. 4 is a schematic block diagram of an embodiment of a grid module 82that includes a control unit 73, a pre-slice manipulator 75, an encoder77, a slicer 79, a post-slice manipulator 81, a pre-slice de-manipulator83, a decoder 85, a de-slicer 87, and/or a post-slice de-manipulator 89.Note that the control unit 73 may be partially or completely external tothe grid module 82. For example, the control unit 73 may be part of thecomputing core at a remote location, part of a user device, part of theDS managing unit 18, or distributed amongst one or more DS storageunits.

In an example of write operation, the pre-slice manipulator 75 receivesa data segment 90-92 and a write instruction from an authorized userdevice. The pre-slice manipulator 75 determines if pre-manipulation ofthe data segment 90-92 is required and, if so, what type. The pre-slicemanipulator 75 may make the determination independently or based oninstructions from the control unit 73, where the determination is basedon a computing system-wide predetermination, a table lookup, vaultparameters associated with the user identification, the type of data,security requirements, available DSN memory, performance requirements,and/or other metadata.

Once a positive determination is made, the pre-slice manipulator 75manipulates the data segment 90-92 in accordance with the type ofmanipulation. For example, the type of manipulation may be compression(e.g., Lempel-Ziv-Welch, Huffman, Golomb, fractal, wavelet, etc.),signatures (e.g., Digital Signature Algorithm (DSA), Elliptic Curve DSA,Secure Hash Algorithm, etc.), watermarking, tagging, encryption (e.g.,Data Encryption Standard, Advanced Encryption Standard, etc.), addingmetadata (e.g., time/date stamping, user information, file type, etc.),cyclic redundancy check (e.g., CRC32), and/or other data manipulationsto produce the pre-manipulated data segment.

The encoder 77 encodes the pre-manipulated data segment 92 using aforward error correction (FEC) encoder (and/or other type of erasurecoding and/or error coding) to produce an encoded data segment 94. Theencoder 77 determines which forward error correction algorithm to usebased on a predetermination associated with the user's vault, a timebased algorithm, user direction, DS managing unit direction, controlunit direction, as a function of the data type, as a function of thedata segment 92 metadata, and/or any other factor to determine algorithmtype. The forward error correction algorithm may be Golay,Multidimensional parity, Reed-Solomon, Hamming, Bose Ray ChauduriHocquenghem (BCH), Cauchy-Reed-Solomon, or any other FEC encoder. Notethat the encoder 77 may use a different encoding algorithm for each datasegment 92, the same encoding algorithm for the data segments 92 of adata object, or a combination thereof.

The encoded data segment 94 is of greater size than the data segment 92by the overhead rate of the encoding algorithm by a factor of X/T, whereX is the width or number of slices, and T is the read threshold. In thisregard, the corresponding decoding process can accommodate at most X-Tmissing EC data slices and still recreate the data segment 92. Forexample, if X=16 and T=10, then the data segment 92 will be recoverableas long as 10 or more EC data slices per segment are not corrupted.

The slicer 79 transforms the encoded data segment 94 into EC data slicesin accordance with the slicing parameter from the vault for this userand/or data segment 92. For example, if the slicing parameter is X=16,then the slicer 79 slices each encoded data segment 94 into 16 encodedslices.

The post-slice manipulator 81 performs, if enabled, post-manipulation onthe encoded slices to produce the EC data slices. If enabled, thepost-slice manipulator 81 determines the type of post-manipulation,which may be based on a computing system-wide predetermination,parameters in the vault for this user, a table lookup, the useridentification, the type of data, security requirements, available DSNmemory, performance requirements, control unit directed, and/or othermetadata. Note that the type of post-slice manipulation may includeslice level compression, signatures, encryption, CRC, addressing,watermarking, tagging, adding metadata, and/or other manipulation toimprove the effectiveness of the computing system.

In an example of a read operation, the post-slice de-manipulator 89receives at least a read threshold number of EC data slices and performsthe inverse function of the post-slice manipulator 81 to produce aplurality of encoded slices. The de-slicer 87 de-slices the encodedslices to produce an encoded data segment 94. The decoder 85 performsthe inverse function of the encoder 77 to recapture the data segment90-92. The pre-slice de-manipulator 83 performs the inverse function ofthe pre-slice manipulator 75 to recapture the data segment 90-92.

FIG. 5 is a diagram of an example of slicing an encoded data segment 94by the slicer 79. In this example, the encoded data segment 94 includesthirty-two bits, but may include more or less bits. The slicer 79disperses the bits of the encoded data segment 94 across the EC dataslices in a pattern as shown. As such, each EC data slice does notinclude consecutive bits of the data segment 94 reducing the impact ofconsecutive bit failures on data recovery. For example, if EC data slice2 (which includes bits 1, 5, 9, 13, 17, 25, and 29) is unavailable(e.g., lost, inaccessible, or corrupted), the data segment can bereconstructed from the other EC data slices (e.g., 1, 3 and 4 for a readthreshold of 3 and a width of 4).

FIG. 6 is a flowchart illustrating an example of updating a directory.The method begins with step 102 where a processing module (e.g., of adispersed storage (DS) processing unit) sends data for storage to adispersed storage network (DSN) memory. For example, the processingmodule dispersed storage error encodes the data to produce a pluralityof sets of encoded data slices and sends the plurality of sets ofencoded data slices to a set of dispersed storage (DS) units of the DSNmemory for storage therein. The method continues at step 104 where theprocessing module determines directory metadata updates of data storeoperation. The directory metadata includes one or more of a directoryfile (e.g., that indicates an association between a filename of the dataand a DSN address), a snapshot file (e.g., that indicates a relationshipbetween at least two snapshots, wherein a snapshot corresponds tocontent of a directory file when the snapshot was generated), and asegment allocation table (SAT) (e.g., which includes DSN addressinformation with regards to the storage of the data). The determinationmay be based on one or more of a new filename associated with the data,a current snapshot pointer (e.g., indicating which snapshot to associatethe data with), and a plurality of DSN addresses associated with theplurality of sets of encoded data slices (e.g., a vault source nameassociated each data segment of a plurality of data segmentscorresponding to each set of the plurality of sets of encoded andslices).

The method continues at step 106 where the processing module updatesdirectory metadata based on the directory metadata updates. For example,the processing module retrieves previous directory metadata (e.g., froma local cache memory) and modifies the previous directory metadata inaccordance with the directory metadata updates to produce the directorymetadata. The method continues at step 108 where the processing modulestores the directory metadata in a local cache memory.

The method continues at step 110 where the processing module determineswhether to synchronize the directory metadata with directory informationstored in the DSN memory. Such directory metadata stored in the localcache memory corresponds to directory information at a local levelutilized by the processing module whereas the directory informationstored in the DSN memory corresponds to directory information at asystem wide level (e.g., utilized by additional processing modules). Thedetermination may be based on one or more of detecting a time intervalsince a last update is greater than a time threshold, an indicator toalways synchronize after a store operation, a data type indicator, afrequency of change indicator, a system activity indicator, a timestampof previous synchronizations, message, and a command. For example, theprocessing module determines to synchronize when the time interval sincethe last update is 60 seconds and the time threshold is 50 seconds. Themethod branches to step 112 when the processing module determines tosynchronize. The method repeats back to step 110 when the processingmodule determines not to synchronize.

The method continues at step 112 where the processing module dispersedstorage error encodes a portion of the directory metadata to produceencoded directory slices. The processing module may select the portionbased on a change indicator since the last update. The method continuesat step 114 where the processing module sends checked write messages toDS units of the DSN memory than include at least some of the encodeddirectory slices, a transaction number corresponding to storing theencoded directory slices, and revision information. The revisioninformation includes a revision number corresponding to the encodeddirectory slices being stored and an expected slice revision numbercorresponding to a last revision number of the encoded directory slicesfrom a viewpoint of the processing module (e.g., aligned with thedirectory metadata stored in the cache memory). The transaction numberassociates two or more steps associated with the storing of data slices.The transaction number may be utilized to facilitate data revisionintegrity when two or more processing modules store similar data to acommon set of DS units. The processing module may generate a newtransaction number based on one or more of a current time indicator anda random number. The DS unit stores an encoded data slice of the checkedwrite message and returns a favorable checked write response message(e.g., a checked write status indicator indicates no error) when theexpected slice revision number is substantially the same as a storedslice revision number. The DS unit does not store the encoded data sliceof the checked write message and returns an unfavorable checked writeresponse message (e.g., the checked write status indicator indicates atleast one error) when the expected slice revision number is notsubstantially the same as the stored slice revision number. Such anunfavorable checked write response message includes the checked writestatus indicator that includes an indication of one or more of slicelocked by another transaction, slice not assigned to the DS unit, theexpected slice revision number does not match the stored slice revisionnumber, and a requester is not authorized to write the slice to the DSunit.

The method continues at step 116 where the processing module receiveschecked write response messages from the DSN memory. The methodcontinues at step 118 where the processing module determines whether thechecked write response messages are favorable based on checked writestatus indicators of the checked write response messages. The methodbranches to step 122 when the processing module determines that thechecked write response messages are not favorable. The method continuesto step 120 when the processing module determines that the checked writeresponse messages are favorable. At step 120, the processing modulesends commit transaction messages to the DSN memory that include thetransaction number associated with storing the encoded directory slices.A DS unit changes a status of at least one encoded directory slice to bevisible for subsequent retrieval when the DS unit receives the committransaction message.

The method continues at step 122 where the processing module recoversthe directory information from the DSN memory when the processing moduledetermines that the checked write response messages are not favorable.For example, the processing module sends read requests to the DSNmemory, receives encoded directory slices, and dispersed storage errordecodes the encoded directory slices to produce the directoryinformation. The method continues at step 124 where the processingmodule determines directory metadata updates based on the directoryinformation. The directory metadata may not include newer updates to thedirectory information. The determination may be based on a receivedupdate flag, a message, the directory information, the directorymetadata, and a comparison of the directory information to the directorymetadata. The method repeats back to step 106 where the processingmodule updates the directory metadata based on the directory metadataupdates.

FIG. 7 is a flowchart illustrating another example of updating adirectory, which includes many similar steps to FIG. 6. The methodbegins with steps 122, 124, 106, and 108 of FIG. 6 where a processingmodule (e.g., of a dispersed storage (DS) processing unit) recover sdirectory information from a dispersed storage network (DSN) memory,determines directory metadata updates based on the directoryinformation, updates directory metadata, and stores the directorymetadata in a cache memory.

The method continues at step 126 where a processing module determinessynchronization status information. The synchronization statusinformation includes at least one of a timer, how many previous failedsynchronization attempts have been made since the last successfulsynchronization, time since last unsuccessful attempt to synchronize,historical synchronization attempts access information, an updatefrequency indicator, a number of users that are authorized to access acommon stored vault, and a service level agreement. The determinationmay be based on one or more of a query, a historical record lookup, amessage, a table lookup, and a command.

The method continues at step 128 where the processing module determineswhether to synchronize based on the synchronization status information.For example, the processing module determines to synchronize when anelapsed time since a last synchronization attempt is above a first timethreshold when a number of consecutive on successful attempts is lessthan an attempt threshold (e.g., attempt more often to start). Asanother example, the processing module determines to synchronize whenthe elapsed time since the last authorization attempt is above a secondtime threshold when the number of consecutive unsuccessful attempts isgreater than the attempt threshold (e.g., attempt less often later). Themethod branches to step 112 of FIG. 6 when the processing moduledetermines to synchronize. The method repeats back to step 128 when theprocessing module determines not to synchronize.

The method continues with steps 114-120 of FIG. 6 where the processingmodule dispersed storage error encodes a portion of the directorymetadata to produce encoded directory slices; sends checked writemessages to the DSN memory that includes encoded directory slices, atransaction number, and revision information; receives checked writeresponse messages; determines whether the checked write responsemessages are favorable; and sends commit transaction messages to the DSNmemory that include the transaction number when the processing moduledetermines that the checked write response messages are favorable. Themethod continues at step 130 where the processing module updates thesynchronization status information when the processing module determinesthat the checked write response messages are not favorable. The updatingmay include one or more of time stamping of a current unsuccessfulattempt to synchronize, incrementing a counter of previous unsuccessfulconsecutive attempts, logging historical error information, andindicating a revisions difference. The method repeats back to step 122of FIG. 6 where the processing module recovers directory informationfrom the DSN memory.

FIG. 8 is a flowchart illustrating an example of synchronizing directoryinformation. The method begins with step 132 where a processing module(e.g., of a dispersed storage (DS) processing unit) segments data toproduce a plurality of data segments in accordance with error codingdispersal storage function parameters. The method continues at step 134where the processing module dispersed storage error encodes a datasegment of the plurality of data segments to produce a set of encodeddata slices utilizing an error coding dispersal storage function. Themethod continues at step 136 where the processing module sends the setof encoded data slices to a set of dispersed storage (DS) units forstorage therein. For example, the processing module sends a set of writerequest messages to the set of DS units that includes the set of encodeddata slices and a first transaction number associated with storing theset of encoded data slices.

The method continues at step 138 where the processing module determinesan estimated time to completion to store the plurality of data segments.The determination may be based on one or more of a storage durationindicator associated with storing slices of a previous data segment, anumber of data segments pending for storage, and an estimationalgorithm. For example, the processing module determines the estimatedtime to completion to be 5 seconds when a first segment was stored in 1second and there are 4 more segments to store.

The method continues at step 140 where the processing module determineswhether to initiate synchronizing directory metadata with directoryinformation of a dispersed storage network (DSN) memory. Thedetermination may be based on one or more of the estimated time tocompletion, an estimated time duration to synchronize, a synchronizationindicator, and a message. For example, the processing module determinesto initiate synchronizing when the estimated time to completion issubstantially the same as the estimated time to synchronize. The methodbranches to step 144 when the processing module determines not toinitiate synchronizing the directory metadata with the directoryinformation of the DSN memory. The method continues to step 142 when theprocessing module determines to initiate synchronizing the directorymetadata with the directory information of the DSN memory.

The method continues at step 142 where the processing module initiatessynchronizing the directory metadata with the directory information ofthe DSN memory. Such a step may be executed once. For example, theprocessing module initiates the synchronizing by modifying the directorymetadata to add a directory entry corresponding to the data, encodingthe directory metadata to produce one or more sets of encoded directoryslices, and sending the one or more sets of encoded directory slices tothe DSN memory for storage utilizing checked write messages that includeencoded directory slices, a second transaction number associated withstoring of the one or more sets of encoded directory slices, andrevision information.

The method continues at step 144 where the processing module determineswhether the plurality of data segments have been stored in the DSNmemory as a plurality of sets of encoded data slices. For example, theprocessing module determines that the plurality of data segments havebeen stored in the DSN memory when the processing module receives atleast a write threshold number of favorable write response messagescorresponding to each set of encoded data slices acknowledgingsuccessful storage of the plurality of sets of encoded data slices. Themethod repeats back to step 134 when the processing module determinesthat the plurality of data segments have not been stored in the DSNmemory. The method continues to step 146 when the processing moduledetermines that the plurality of data segments have been stored in theDSN memory.

The method continues at step 146 where the processing module determineswhether synchronization of the directory metadata with the directoryinformation is complete. For example, the processing module determinesthat the synchronization is complete when the processing module receivesat least a write threshold number of favorable write response messagescorresponding to each set of encoded directory slices of the one or moresets of encoded directory slices acknowledging successful storage of theone or more sets of encoded directory slices. The method branches tostep 150 when the processing module determines that the synchronizationis complete. The method continues to step 148 when the processing moduledetermines that the synchronization is not complete.

The method continues at step 148 where the processing modulesynchronizes the directory metadata with the directory information ofthe DSN memory. The processing module may continue the process (e.g.,writing encoded directory slices) when the processing module hadpreviously initiated synchronizing the directory metadata with thedirectory information. The processing module initiates the synchronizingof the directory metadata with the directory information when theprocessing module had not previously initialized the synchronizing(e.g., when the data segments have been stored but the synchronizationhad not been started). The method repeats back to step 146 where theprocessing module determines whether the synchronization of thedirectory metadata with the directory information is complete. Themethod continues at step 150 where the processing module sends committransaction messages to the DSN memory that includes the firsttransaction number and the second transaction number to completesynchronization of the data storage and the associated directoryinformation when the processing module determines that thesynchronization of the directory metadata with the directory informationis complete.

FIG. 9 is a flowchart illustrating another example of synchronizingdirectory information. The method begins with step 152 where aprocessing module (e.g., of a dispersed storage (DS) processing unit)determines whether to verify directory metadata. The determination maybe based on one or more of a timer associated with a metadata entry, atime threshold, a directory access frequency indicator, and accessfrequency threshold, a conflicts frequency indicator, a conflictsthreshold, an average system loading indicator, a system loadingthreshold, an overall timer, and a overall time threshold. For example,the processing module determines to verify the directory metadata when atimer associated with the metadata entry file name stuff.txt is greaterthan a time threshold. The method repeats back to step 152 when theprocessing module determines to not verify the directory metadata. Themethod continues to step 154 when the processing module determines toverify the directory metadata.

The method continues at step 154 where the processing module sends readrequest messages to a dispersed storage network (DSN) memory withregards to directory information. For example, the processing modulesends read request messages to dispersed storage (DS) units of the DSNmemory to retrieve the directory information such that a DS unit sendsthe processing module an encoded data slice corresponding to a readrequest message in response. As another example, the processing modulesends checked read request messages to DS units of the DSN memory,wherein the checked read request messages includes an expected revisionnumber to retrieve the directory information such that a DS unit sendsthe processing module an encoded data slice corresponding to a checkedread request message in response when the encoded data slice correspondsto a stored slice revision number different than the revision number. Assuch, network resources may not be utilized between the DS unit and theprocessing module to send an encoded data slice when the stored encodeddata slice is substantially the same as what is expected (e.g., storedas directory metadata in a local cache memory associated with theprocessing module).

The method continues at step 156 where the processing module determineswhether the directory metadata compares favorably to the directoryinformation. The determination may be based on one or more of comparingreceived directory information (e.g., received directory informationproduced from decoded received directory slices) to the directorymetadata and a checked read response message that indicates a revisionassociated with the directory information is substantially the same as arevision associated with the directory metadata. For example, theprocessing module determines that the directory metadata comparesfavorably to the directory information when the received directoryinformation from the DSN memory is substantially the same as thedirectory metadata. As another example, the processing module determinesthat the directory metadata compares favorably to the directoryinformation when the checked read response message indicates thatrevision 430 is associated with the directory information and revision430 is also associated with the directory metadata.

The method repeats back step 152 when the processing module determinesthat the directory metadata compares favorably to the directoryinformation. The method continues to step 158 when the processing moduledetermines that the directory metadata does not compare favorably to thedirectory information. The method continues at step 158 where theprocessing module updates the directory metadata based on the directoryinformation. For example, the processing module selects new entries ofthe directory information that do not match items of the directorymetadata to update the directory metadata.

FIG. 10A is a diagram illustrating an example of a snapshot file 160 andof a directory file 162 relationship. Such a snapshot file 160 includesa current snapshot field, 164, a children field 166, and a timestampfield 168. The directory file 162 includes one or more directory fileentries, wherein a directory file entry includes a file identifier (ID)and an association with one or more snapshot IDs. For example, one ormore file IDs are listed for each associated snapshot ID. As anotherexample, one or more snapshot IDs are listed for each associated fileID.

The parent snapshot field 164 includes a parent snapshot ID associatedwith a parent snapshot where the parent snapshot may include a parentrelationship with one or more other children snapshots. The childrenfield 166 includes one or more children snapshot IDs associated withchildren snapshots where the children snapshots include a childrelationship with a parent snapshot. The timestamp field 168 includes atimestamp corresponding to when the parent snapshot of the snapshot fileentry was created. FIGS. 10A-10H illustrate examples of an associatedsnapshot file and at least one corresponding directory file as exampleevents occur at various successive times. Such events may include addinga snapshot, deleting a snapshot, adding a directory entry, and deletinga directory entry. The method of operation to modify the snapshot fileand the at least one directory file is further discussed with referenceto FIGS. 11A, 11B, 12A, and 12B.

Note that FIG. 10A represents the snapshot file 160 and the directoryfile 162 subsequent to a starting point at time=0 (e.g., timestamp t=0)where a parent snapshot ID=root is added at t=0, wherein the parentsnapshot root has no children and the associated directory fileindicates that files ip.txt and CS289.doc are associated with thesnapshot root. Allowed access to snapshot root implies that access tothe files ip.txt and CS289.doc are enabled.

FIG. 10B is a diagram illustrating another example of a snapshot file160 and a directory file 170 relationship at t=1 where a file with afile ID of CS281.doc is added to the directory file for snapshot root.Allowed access to snapshot root implies that access to files ip.txt,CS289.doc, and CS281.doc is enabled.

FIG. 10C is a diagram illustrating another example of a snapshot file172 and a directory file 170, 174 relationship subsequent to t=2 where asnapshot ID=foo is added at t=2, wherein snapshot foo is both a parentsnapshot with no children and a child snapshot of the parent snapshotroot. Each file associated with the parent snapshot root at the time ofcreating the snapshot foo is now associated with the snapshot foo.Allowed access to snapshot root still implies that access to filesip.txt, CS289.doc, and CS281.doc is enabled and that allowed access tosnapshot foo implies that access to files ip.txt, CS289.doc, andCS281.doc is enabled. Further note that while FIG. 10C illustratesdirectory files 170 and 174 associating file names by snapshot, a singledirectory file may be utilized that associates snapshots with eachfilename. As a specific example, file ip.txt is associated with thesnapshot root and the snapshot foo.

FIG. 10D is a diagram illustrating another example of a snapshot file172 and a directory file 170 and 182 relationship at t=3 where a filewith a file ID of CS400.doc is added to the directory file 182 forsnapshot foo. Allowed access to snapshot root still implies that accessto files ip.txt, CS289.doc, and CS281.doc is enabled and that allowedaccess to snapshot foo implies that access to files ip.txt, CS289.doc,CS281.doc, and CS400.doc is enabled. Access to snapshot root does notimply that access to file CS400.doc is enabled (e.g., a parent snapshotdoes not inherit access to files associated with an associated childsnapshot).

FIG. 10E is a diagram illustrating another example of a snapshot file172 and a directory file 184 and 182 relationship at t=4 where fileip.txt is deleted from the directory file 182 for snapshot root. Allowedaccess to snapshot root still implies that access to files CS289.doc andCS281.doc is enabled (but not ip.txt) and that allowed access tosnapshot foo still implies that access to files ip.txt, CS289.doc,CS281.doc, and CS400.doc is enabled. A child snapshot retains access tofiles that are unassociated from an associated parent snapshot.

FIG. 10F is a diagram illustrating another example of a snapshot file172 and a directory file 186 and 182 relationship at t=5 where a filewith a file ID of blah.txt is added to the directory file 186 forsnapshot root. Allowed access to snapshot root implies that access tofiles CS289.doc, CS281.doc, and blah.txt is enabled and that allowedaccess to snapshot foo implies that access to files ip.txt, CS289.doc,CS281.doc, and CS400.doc is enabled (but not blah.txt). Access to a fileassociated with a parent by a child after the child was created is notallowed, e.g., access to snapshot foo does not imply that access to fileblah.txt is enabled since file blah.txt was added to snapshot root afterthe child snapshot foo was created.

FIG. 10G is a diagram illustrating another example of a snapshot file188 and a directory file 186, 182, and 190 relationship subsequent tot=6 where a snapshot ID=bar is added at t=6, wherein snapshot bar isboth a parent snapshot with no children and a child snapshot of parentsnapshot foo. Each file associated with the parent snapshot and upwards(e.g., all parents of the parent) at the time of creating the snapshotbar is now associated with the snapshot bar. Allowed access to snapshotroot still implies that access to files CS289.doc, CS281.doc, andblah.txt is enabled; allowed access to snapshot foo still implies thataccess to files ip.txt, CS289.doc, CS281.doc, and CS400.doc is enabled;and allowed access to snapshot bar implies that access to files ip.txt,CS289.doc, CS281.doc, CS400.doc, and blah.txt is enabled.

FIG. 10H is a diagram illustrating another example of a snapshot file188 and a directory file 186, 182 and 198 relationship at t=7 where afile with a file ID of CS500.doc is added to the directory file 198 forsnapshot bar. Allowed access to snapshot root still implies that accessto files CS289.doc, CS281.doc, and blah.txt is enabled; allowed accessto snapshot foo still implies that access to files ip.txt, CS289.doc,CS281.doc, and CS400.doc is enabled; and allowed access to snapshot barimplies that access to files ip.txt, CS289.doc, CS281.doc, CS400.doc,blah.txt, and CS500.doc is enabled. No upward parent snapshots inheritaccess to files associated with an associated child snapshot as filesare added to the child snapshot. For example, access to the fileCS500.doc is not enabled for snapshot root and snapshot foo.

FIG. 11A is a flowchart illustrating an example of adding a snapshot.The method begins with step 200 where a processing module (e.g., of adispersed storage (DS) processing unit) receives an add snapshotrequest. The add snapshot request includes one or more of a parentsnapshot identifier (ID), a timestamp, a read-only indicator, an activesnapshot indicator, a vault ID, and a snapshot ID. The processing modulemay authorize the request by comparing a received requester ID with anauthorized ID and authorizing the request when the received requester IDand be authorized ID are substantially the same. The method continueswhen the processing module authorizes the request.

The method continues at step 202 where the processing module determinesa parent snapshot when the request is authorized. The determination maybe based on one or more of receiving the parent snapshot ID, receivingthe active snapshot indicator, a vault ID, a list, a message, and aquery. The method continues at step 204 where the processing modulerecovers a snapshot file. The recovering includes determining a snapshotfile dispersed storage network (DSN) address based on the vault ID,sending read requests messages with regards to encoded snapshot fileslices to a DSN memory, receiving read response messages that includeencoded snapshot file slices, and dispersed storage error decoding theencoded snapshot file slices to produce the snapshot file.

The method continues at step 206 where the processing module modifiesthe snapshot file to include a new snapshot. The modification to thesnapshot file includes one or more of adding the snapshot ID (e.g., fromthe request) as a child snapshot to the determined parent snapshot,creating a timestamp from a real-time indicator, adding the childsnapshot ID as a parent snapshot ID with no children, and indicatingwhether the snapshot is read-only based on the read-only indicator ofthe requests. The method continues at step 208 where the processingmodule saves the modified snapshot file. The saving includes dispersedstorage error encoding the modified snapshot file to produce encodedmodified snapshot file slices and sending the modified snapshot fileslices to the DSN memory for storage therein.

The method continues at step 210 where the processing module recoversdirectory file information based on snapshot file information of thesnapshot file. The recovering includes determining one or more directoryfile DSN addresses based on the snapshot ID in the vault ID, sendingread requests messages with regards to encoded directory slices to theDSN memory utilizing the one or more directory file DSN addresses,receiving read response messages that include encoded directory slices,and dispersed storage error decoding the encoded directory slices toproduce the directory file information. Note that the processing modulerecovers each directory file entry (e.g., each file name) associatedwith all parent snapshots of the new snapshot.

The method continues at step 212 where the processing module modifiesthe directory file information to associate the new snapshot with thedirectory file information (e.g., all filenames associated with parentsnapshots of the new snapshot). The new snapshot enables access to allfiles associated with all parents of the new snapshot. The methodcontinues at step 214 where the processing module saves the modifieddirectory file information. The processing module may add a newdirectory file associated with the new snapshot and/or modify anexisting directory file in accordance with the modified directory fileinformation. Saving the modified directory file information includesdispersed storage error encoding the modified directory file informationto produce encoded modified directory file slices and sending theencoded modified directory file slices to the DSN memory for storagetherein.

FIG. 11B is a flowchart illustrating an example of deleting a snapshot,which includes many similar steps to FIG. 11A. The method begins withstep 216 where a processing module (e.g., of a dispersed storage (DS)processing unit) receives a delete snapshot request. The delete snapshotrequest includes one or more of a parent snapshot identifier (ID), atimestamp, a read-only indicator, an active snapshot indicator, a vaultID, and a snapshot ID. The method continues with step 204 of FIG. 11Awhere the processing module recovers the snapshot file. The methodcontinues at step 218 where the processing module modifies the snapshotfile to link any children of the snapshot to a parent of the snapshot.As such, a grandparent snapshot becomes the parent snapshot of each ofthe children of the deleted snapshot. The method continues at step 220where the processing module modifies the snapshot file to exclude (e.g.,delete) the snapshot. The method continues with step 208 of FIG. 11A tosave the modified snapshot file.

The method continues at step 222 where the processing module recovers adirectory file associated with the snapshot corresponding to a vaultassociated with the snapshot to be deleted. The method continues at step224 where the processing module modifies the directory file todisassociate the snapshot with directory file information. For example,the processing module modifies the directory file information such thatassociated directory file entries are no longer linked to the snapshotbeing deleted. The processing module may perform this task as abackground activity. The method continues at step 226 where theprocessing module modifies the directory file to delete any directoryentries no longer associated with any snapshots (e.g., completely removethe directory entries when there are no snapshots associated with thedirectory entries). The processing module may perform this task as abackground activity. The method continues with step 214 of FIG. 11Awhere the processing module saves the modified directory file.

FIG. 12A is a flowchart illustrating another example of updating adirectory, which includes similar steps to FIGS. 11A-B. The methodbegins with step 228 where a processing module (e.g., of a dispersedstorage (DS) processing unit) receives an add directory entry request.The directory request includes one more of a snapshot identifier (ID), atimestamp, a directory ID, a directory entry, a file ID, a source name,and active snapshot indicator, and a vault ID. The method continues atstep 230 where the processing module determines a snapshot. Thedetermination may be based on one or more of receiving a snapshot ID,receiving an active snapshot indicator, a vault ID, a list, a message,and a query. For example, the processing module determines the snapshotbased on receiving the snapshot ID in the add directory entry request.

The method continues with step 222 of FIG. 11B where the processingmodule recovers a directory file associated with the snapshot. Themethod continues at step 232 where the processing module modifies thedirectory file to add a new directory file entry. For example, theprocessing module adds a new filename and/or a source name to thedirectory information of the directory file. The method continues atstep 234 where the processing module modifies the directory file toassociate the snapshot with the new directory entry. For example, theprocessing module links the new filename to the snapshot ID but not toother snapshots. The method continues with step 214 of FIG. 11A wherethe processing module saves the modified directory file.

FIG. 12B is a flowchart illustrating another example of updating adirectory, which includes similar steps to FIGS. 11A, 11B, and 12A. Themethod begins with step 236 where a processing module (e.g., of adispersed storage (DS) processing unit) receives a delete directoryentry request. The delete directory request includes one more of asnapshot identifier (ID), a timestamp, a directory ID, a directoryentry, a file ID, a source name, and active snapshot indicator, and avault ID. The method continues with step 230 of FIG. 12A where theprocessing module determines a snapshot. The method continues with step222 of FIG. 11B where the processing module recovers a directory fileassociated with the snapshot. The method continues at step 238 where theprocessing module modifies the directory file to disassociate thesnapshot with a directory entry. For example, the processing modulemodifies the directory file to no longer link the snapshot to thedirectory entry. The directory entry may still be linked to othersnapshots. The method continues at step 240 where the processing modulemodifies the directory file to delete the directory entry when nosnapshots are associated with the directory entry. The method continueswith step 214 of FIG. 11A where the processing module saves the modifieddirectory file.

FIG. 13 is a flowchart illustrating an example of storing data. Themethod begins with step 242 where a processing module (e.g., of adispersed storage (DS) processing unit) receives data for storage. Thereceiving may include receiving one or more of the data, a dataidentifier (ID), a data type indicator, a file size indicator, and astorage requirement. The method continues at step 244 where theprocessing module determines a data portion of the data and a dataportion ID. The determination may be based on one or more of the filesize indicator, an upload speed indicator, the system performanceindicator, an estimated duration of an upload, a duration threshold, thedata type indicator, and the storage requirement. For example, theprocessing module determines the data portion to include 500 MB when thefile size indicator indicates 5 GB, the estimated duration of the uploadis 30 seconds, and the duration threshold is 2 seconds.

The method continues at step 246 where the processing module dispersedstorage error encodes the data portion to produce encoded data slices.Alternatively, the processing module produces multiple sets of encodeddata slices. The method continues at step 248 where the processingmodule stores the encoded data slices in a dispersed storage network(DSN) memory. For example, the processing module sends write requestmessages that includes the encoded data slices to the DSN memory andreceives at least a write threshold number of favorable write responsemessages for each set of encoded data slices from the DSN memory.

The method continues at step 250 where the processing module updatesdirectory metadata to include the data portion ID. The processing modulemay append a file extension to a filename or file ID associated with thedata to indicate that the data portion is a portion and not all of thedata. For example, the processing module appends an in-progressextension to the file name and stores the directory metadata in a cachememory. The method continues at step 252 where the processing moduledispersed storage error encodes the directory metadata to produceencoded directory slices. Alternatively, the processing module producesmultiple sets of encoded directory slices. The method continues at step254 where the processing module stores the encoded directory slices inthe DSN memory. For example, processing module sends write requestmessages that includes the encoded directory slices to the DSN memoryand receives at least a write threshold number of favorable writeresponse messages for each set of encoded directory slices from the DSNmemory.

The method continues at step 256 where the processing module facilitatescommitting the encoded data slices and encoded directory slicesutilizing a common commit transaction message. The common committransaction message includes a first transaction number associated withthe encoded data slices and a second transaction number associated withthe encoded directory slices. The processing module sends the commoncommit transaction message to the DSN memory.

The method continues at step 258 where the processing module determineswhether all the data has been stored based on comparing data portionsstored to all of the data. The processing module determines that all thedata has been stored when all the portions stored so far aresubstantially the same as all the data. The method repeats back to step244 when the processing module determines that all the data has not beenstored. The method continues to step 260 when the processing moduledetermines that all the data has been stored.

The method continues at step 260 where the processing module updates thedirectory metadata to exclude one or more data portion ID sent toinclude a data ID. For example, the processing module eliminates thetemporary file extension associated with the ID of the data. The methodcontinues at step 262 where the processing module facilitates storingand committing the updated directory metadata as encoded directoryslices in the DSN memory. For example, the processing module encodes theupdated directory metadata to produce encoded directory slices, sends awrite request message to the DSN memory that includes the encodeddirectory slices, and sends a commit transaction request message to theDSN memory.

FIG. 14A is a flowchart illustrating another example of storing data.The method begins with step 264 where a processing module (e.g., of adispersed storage (DS) processing unit) dispersed storage error encodesdata to produce a plurality of sets of encoded data slices. The methodcontinues at step 266 where the processing module updates directorymetadata regarding storing the data as the plurality of sets of encodeddata slices in a dispersed storage network (DSN) memory to produceupdated directory metadata. The updating the directory metadata includesretrieving the directory metadata from at least one of the DSN memoryand a local memory (e.g., a cache memory), determining a DSN memorystorage location information for the plurality of sets of encoded dataslices, and modifying the directory metadata to include a filenameassociated with the data and the DSN memory storage location to producethe updated directory metadata. The DSN memory storage locationinformation includes one or more of: a source name corresponding to aDSN memory storage location, a data size indicator, a data typeindicator, snapshot information (e.g., a snapshot file, a snapshotpointer), a timestamp, and a segment allocation table (e.g., thatincludes a start segment vault source name, a segment size, asegmentation approach, and a total length for each region).

The method continues at step 268 where the processing module dispersedstorage error encodes the updated directory metadata to produce aplurality of sets of encoded directory metadata slices. The methodcontinues at step 270 where the processing module transmits one or moredata slice write requests to the DSN memory regarding storing theplurality of sets of encoded data slices, wherein the one or more dataslice write requests includes a first transaction number.

The transmitting the one or more data slice write requests includesgenerating a set of data slice write requests, wherein each of the dataslice write requests includes the first transaction number regardingstorage of a respective group of encoded data slices of the plurality ofsets of encoded data slices and transmitting the set of data slice writerequests to a set of dispersed storage (DS) units of the DSN memory. Thegroup of encoded data slices may include one or more of a set of encodeddata slices, a portion of a set of encoded data slices, encoded dataslices associated with a common pillar, and encoded data slicesassociated with at least two common pillars. Alternatively, or inaddition to, the transmitting the one or more data slice write requestsincludes generating a data slice write request, wherein the data slicewrite request includes the first transaction number regarding storage ofthe plurality of sets of encoded data slices and transmitting the set ofdata slice write requests to a set of dispersed storage (DS) units ofthe DSN memory, wherein a DS unit of the set of DS units is targeted tostore a respective group of encoded data slices of the plurality of setsof encoded data slices.

The method continues at step 272 where the processing module transmitsone or more directory metadata write requests to the DSN memoryregarding storing the plurality of sets of encoded directory metadataslices, wherein the one or more directory metadata write requestsincludes a second transaction number. The method continues at step 274where the processing module transmits one or more commit requests to theDSN memory, when a favorable write response condition exists, for atleast one of: the one or more data slice write requests and the one ormore directory metadata write requests, to commit storage of at leastone of: the plurality of sets of encoded data slices and the pluralityof sets of encoded directory metadata slices, wherein the commit requestincludes the first transaction number and the second transaction number.

For example, the processing module receives at least a threshold numberof data slices write responses regarding the one or more data slicewrite requests and generates a commit request as the one or more commitrequests. As another example, the processing module receives at least athreshold number of directory metadata write responses regarding the oneor more directory metadata write requests and generates the commitrequest. As yet another example, the processing module receives at leasta first threshold number of data slices write responses regardingwriting a first set of encoded data slices of the plurality of sets ofencoded data slices and generates a first commit request as one of theone or more commit requests. As a still further example, the processingmodule receives at least a first threshold number of directory metadatawrite responses regarding writing a first set of encoded directorymetadata slices of the plurality of sets of encoded directory metadataslices and generates the first commit request. As yet an even furtherexample, the processing module receives at least a second thresholdnumber of data slices write responses regarding writing a second set ofencoded data slices of the plurality of sets of encoded data slices andgenerates a second commit request as a second one of the one or morecommit requests.

The transmitting one or more commit requests includes one of generatinga common commit request as the one or more commit requests to include acommon first transaction number and a common second transaction numberregarding committing storage of the plurality of sets of encoded dataslices and the plurality of sets of encoded directory metadata slicesand generating a group of commit requests as the one or more commitrequests, wherein a commit request of the group of commit requestsincludes a unique first transaction number and a unique secondtransaction number regarding committing storage of a respective group ofencoded data slices of the plurality of sets of encoded data slices.Such storing of the data and the updated directory metadata may providea synchronization system improvement.

FIG. 14B is a block diagram of a dispersed storage (DS) module thatoperates within one or more DS units to store data in accordance withthe method described in FIG. 14A. The DS module 278 includes an encodedata module 282, an encoded metadata module 284, a transmit slicesmodule 286, a transmit commit module 288, and a write response receivingmodule 290. The modules 282-290 may be separate modules, may besub-modules of another module, and/or a combination thereof.

The encode data module 282 dispersed storage error encodes data 292(e.g., retrieved data, received data, generated data) to produce aplurality of sets of encoded data slices 294. The encode metadata module284 updates directory metadata regarding storing the data 292 as theplurality of sets of encoded data slices 294 in a dispersed storagenetwork (DSN) memory 22 (e.g., in at least one dispersed storage (DS)unit 36) to produce updated directory metadata and dispersed storageerror encoding the updated directory metadata to produce a plurality ofsets of encoded directory metadata slices 300.

The encode metadata module 284 is operable to update the directorymetadata by retrieving the directory metadata 296 and/or 298 from theDSN memory 22 (e.g., directory metadata 296) and/or a local memory 280(e.g. directory metadata 290). The updating further includes determiningDSN memory storage location information for the plurality of sets ofencoded data slices. The DSN memory storage location informationincludes one or more of: a source name corresponding to a DSN memorystorage location, a data size indicator, a data type indicator, snapshotinformation, a timestamp; and a segment allocation table, and modifyingthe directory metadata to include a filename associated with the dataand the DSN memory storage location to produce the updated directorymetadata.

The transmit slices module 286 facilitates transmitting one or more dataslice write requests 302 to the DSN memory 22 regarding storing theplurality of sets of encoded data slices 294, wherein the one or moredata slice write requests 302 includes a first transaction number 304and facilitates transmitting one or more directory metadata writerequests 306 to the DSN memory 22 regarding storing the plurality ofsets of encoded directory metadata slices 300, wherein the one or moredirectory metadata write requests 306 includes a second transactionnumber 308. The transmit slices module 286 module is operable totransmit the one or more data slice write requests 302 by generating aset of data slice write requests, wherein each of the data slice writerequests includes the first transaction number 304 regarding storage ofa respective group of encoded data slices of the plurality of sets ofencoded data slices 294 and transmitting the set of data slice writerequests to a set of dispersed storage (DS) units of the DSN memory 22.The transmit slices module 286 is further operable to transmit the oneor more data slice write requests 302 by generating a data slice writerequest, wherein the data slice write request includes the firsttransaction number 304 regarding storage of the plurality of sets ofencoded data slices 294 and transmitting the set of data slice writerequests to a set of dispersed storage (DS) units of the DSN memory 22,wherein a DS unit 36 of the set of DS units is targeted to store arespective group of encoded data slices of the plurality of sets ofencoded data slices 294.

The transmit commit module 288 transmits one or more commit requests 310to the DSN memory 22, when a favorable write response condition exists(e.g., receiving a favorable write response condition indicator 314),for at least one of: the one or more data slice write requests and theone or more directory metadata write requests, to commit storage of atleast one of: the plurality of sets of encoded data slices 294 and theplurality of sets of encoded directory metadata slices 300, wherein thecommit request 310 includes the first transaction number 304 and thesecond transaction number 308. The transmit commit module 288 isoperable to transmit one or more commit requests 310 by one ofgenerating a common commit request as the one or more commit requests toinclude a common first transaction number and a common secondtransaction number regarding committing storage of the plurality of setsof encoded data slices 294 and the plurality of sets of encodeddirectory metadata slices 300 and generating a group of commit requestsas the one or more commit requests 310, wherein a commit request of thegroup of commit requests includes a unique first transaction number anda unique second transaction number regarding committing storage of arespective group of encoded data slices of the plurality of sets ofencoded data slices 294.

The write response receiving module 290 facilitates receiving at least athreshold number of data slices write responses 312 regarding the one ormore data slice write requests 302 and generating a commit request asthe one or more commit requests 310 and/or facilitates receiving atleast a threshold number of directory metadata write responses 312regarding the one or more directory metadata write requests 306 andgenerating the commit request. The receiving at least the thresholdnumber of data slices write responses 312 may include generating thefavorable write response condition indicator 314 when the at least thethreshold number of data slices write responses 312 are received.

Alternatively, or in addition to, the write response receiving module290 facilitates at least one of receiving at least a first thresholdnumber of data slices write responses 312 regarding writing a first setof encoded data slices of the plurality of sets of encoded data slices294 and generating a first commit request as one of the one or morecommit requests 310, receiving at least a first threshold number ofdirectory metadata write responses 312 regarding writing a first set ofencoded directory metadata slices of the plurality of sets of encodeddirectory metadata slices 300 and generating the first commit request,and receiving at least a second threshold number of data slices writeresponses 312 regarding writing a second set of encoded data slices ofthe plurality of sets of encoded data slices 294 and generating a secondcommit request as a second one of the one or more commit requests 310.

FIG. 15 is a diagram illustrating an example of a segmentationallocation table 320 (SAT) that includes a plurality of regions 1-R.Each region of the plurality of regions 1-R includes a start segmentvault source name field 322, a segment size field 324, a segmentationapproach field 326, and a total length field 328. The start segmentvault source name field 322 includes a vault source name correspondingto a first data segment of a contiguous number of data segments thatstore data corresponding to a region. Alternatively, or in addition to,the start segment vault source name field 322 may include a fileidentifier (ID), a segment ID, a block ID and a file type indicator(e.g., block storage or file storage). The segment size field 324includes a segment size entry corresponding to a number of bytes of eachsegment associated with the region.

The segmentation approach field 326 includes a segmentation approachindicator, which indicates what type of segmentation is utilized whensegmenting data to produce the contiguous number of data segmentsassociated with the region. For example, segment sizes of the contiguousnumber of data segments are substantially the same when the segmentationapproach indicator indicates a flat or fixed approach. As anotherexample, segment sizes of the contiguous number of data segments startsmall and ramp up when the segmentation approach indicator indicates aramp up approach. As yet another example, segment sizes of thecontiguous number of data segments start archer and ramp down when thesegmentation approach indicator indicates a ramp down approach. In suchramping approaches, the segmentation approach field 326 may also includea starting segment size, a size increment number (e.g., the differencein size between segments), and a ramp up/down indicator. The totallength field 328 includes a length indicator (e.g., a number of bytes)corresponding to an amount of data stored in the contiguous number ofdata segments that store data corresponding to the region.Alternatively, or in addition to, the total length field 328 may includea data total length indicator corresponding to an amount of data storedin all regions associated with the data.

The SAT may be stored in a local memory associated to enable access to adispersed storage network (DSN) memory and/or as a SAT data segment inthe DSN memory (e.g., as a set of encoded SAT slices). Note that a SATvault source name is associated with the SAT when the SAT is stored inthe DSN memory utilizing the SAT vault source name. At least one SATassociates data to one or more regions of contiguous data segments,wherein each data segment of the one or more contiguous data segments isstored as a set of encoded data slices in a dispersed storage network(DSN) memory. For example, an initial store of a file stuff.txt resultsin a first region stored in the DSN memory that includes four contiguousdata segments of the initial data of stuff.txt and one data segmentcorresponding to the SAT. Next, a second store of more data of the filestuff.txt results in a second region stored in the DSN memory thatincludes four more contiguous data segments of appended data ofstuff.txt and an updated SAT data segment. The SAT vault source nameenables access to all of the encoded data slices associated with thedata. The format of the vault source names of the SAT and the contiguousnumber of data segments is discussed in greater detail with reference toFIGS. 16A-C. A method to segment data and creating a SAT is discussed ingreater detail with reference to FIG. 17.

FIG. 16A is a diagram illustrating an example of a slice name format.This listing format includes a slice name field 330. The slice namefield 330 includes a slice index field 332 and a vault source name field334. The slice index field 332 includes a slice index entry that may beutilized to produce a pillar number corresponding to a dispersed storage(DS) unit to store an associated encoded data slice. The vault sourcename field 334 includes a vault source name entry that includes a sourcename field 336 and a segment number field 338. The segment number field338 includes a segment number entry that corresponds to a segmentidentifier (ID) for each segment associated with storing data and/or asegment allocation table (SAT). For example, segment number zero isassociated with a SAT and segment number one is associated with a firstsegment of a contiguous number of segments associated with a firstregion of data. As a specific example, a region 1 SAT is assigned asource name of AAA and a segment number of 0 to produce a vault sourcename of AAA0 and an affiliated first segment of data is associated withthe same source name of AAA and a segment number of 1 to produce a vaultsource name of AAA1. As another specific example, a region 2 SAT isassigned a source name of BBB and a segment number of 0 to produce avault source name of BBB0 and an affiliated fifth segment of the data isassociated with the source name of BBB and a segment number of 5 toproduce a vault source name of BBB5.

The source name field 336 includes a source name entry that includes avault ID field 340, a generation field 342, and an object number field344. The vault ID field 340 includes a vault ID entry that associates aplurality of data as a group of data accessible when access to such avault is enabled. The generation field 342 includes a generation entrythat associates a subgroup of data associated with the vault ID. Forexample, successive generations may be added over time to organize datainto multiple subgroups. The object number (e.g., a file ID) field 344includes a object number entry that identifies the data and may becreated based on one or more of a filename, a hash of the data, a hashof the filename, a user ID, a vault ID, and a random number.

FIG. 16B is a diagram illustrating an example of data segmentation thatincludes a segment allocation table (SAT) 320 and a plurality ofconsecutive segments 1-4 corresponding to initially storing data as afirst region. In an example, the SAT 320 is stored in a dispersedstorage network (DSN) memory at a vault source name address of AAA0. TheSAT 320 includes a start segment vault source name field 322 with anentry of AAA1, a segment size field 324 entry of 100 bytes, a fixedsegmentation approach field 326 entry of, and a total length field 328entry of 340 bytes. Each of the segments 1-4 contains a maximum of 100bytes in accordance with the segment size of 100 bytes as indicated inthe SAT. Segments 1-3 each contain 100 bytes and segment 4 contains 40bytes in accordance with the total length of 340 bytes as indicated by atotal length entry of a total length field 328 of the SAT. Segment 1 isstored in the DSN memory at a vault source name address of AAA1 inaccordance with the start segment vault source name AAA1 as indicated inthe SAT. Segments 2-4 are stored in the DSN memory at vault source nameaddresses of AAA2-AAA4 in accordance with contiguous segment numbering.

FIG. 16C is a diagram illustrating another example of data segmentationthat includes a segment allocation table (SAT) 320 a plurality ofconsecutive segments 5-8 corresponding to a second storing data as asecond region (e.g., data appended to a first region). In an example,the SAT is stored in a dispersed storage network (DSN) memory at a vaultsource name address of BBB0 The SAT includes two regions, wherein afirst region includes a start segment vault source name of AAA1, asegment size of 100 bytes, a fixed segmentation approach, and a totallength of 340 bytes. The second region includes a start segment vaultsource name of BBB5, a segment size of 300 bytes, a fixed segmentationapproach, and a total length of 1200 bytes. Each of the segments 5-8contains a maximum of 300 bytes in accordance with the segment size of300 bytes as indicated in the SAT. Segments 5-8 each contain 300 bytesin accordance with the total length of 1200 bytes as indicated in theSAT. Segment 5 is stored in the DSN memory at a vault source nameaddress of BBB5 in accordance with the start segment vault source nameBBB5 as indicated in the SAT. The segment number 5 is next sequentiallyafter segment 4 of the first region as illustrated in FIG. 16B. Segments5-8 are stored in the DSN memory at vault source name addresses ofBBB5-BBB8 in accordance with contiguous segment numbering. A SATassociated with region 1 (e.g., as discussed with reference to FIG. 16B)may be deleted when the SAT associated with region 2 is stored, whereinthe SAT associated with region 2 includes the region 1 information.Alternatively, the SAT includes information associated with region 2 andnot with region 1.

FIG. 17A is a flowchart illustrating an example of segmenting data. Themethod begins with step 350 were a processing module (e.g., a dispersedstorage (DS) module) receives data of a file for storage in a dispersedstorage network (DSN) memory (e.g., new data of a new filename,additional data of an existing filename). The method continues at step352 where the processing module determines a segmentation scheme forstoring the data. The segmenting scheme includes a segment size (e.g.,based on one or more of total length of the plurality of data segmentsand/or a next address) and a segmentation approach. For example, thesegmenting scheme includes a fixed segmentation approach and acorresponding fixed segment size such that each of the plurality of datasegments has a size no greater than the fixed segment size (e.g., whensegment size=data size/number of segments). As another example,segmenting scheme includes a varying segmentation approach and aninitial segment size such that a data segment of the plurality of datasegments has a size corresponding to the initial segment size andremaining data segments of the plurality of data segments have a sizebased on the initial segment size and the varying segmentation approach.The determining the segmentation scheme is based on one or more of aprevious segmentation scheme (e.g., a previous segmentation schemeutilized for storing other data associated with the data), a data sizeindicator, a data type indicator, a storage requirement, a vaultidentifier (ID), a lookup, a message, and a query.

The method continues at step 354 whether processing module determineshow to store the data in accordance with the segmentation scheme toproduce information for storing the data. The information for storingthe data includes a start segment vault source name (e.g., an availableaddress for a first data segment) and a total length of the data (e.g.,based on one of a data size indicator, counting bytes). The methodcontinues at step 356 for the processing module generates an entrywithin a segment allocation table associated with the file, wherein theentry includes the information for storing the data and the segmentationscheme.

The method continues at step 358 where the processing module facilitatesstorage of the segment allocation table in the DSN memory. Thefacilitating storage of the segment allocation table includes obtaininga segment allocation table vault source name (e.g., a directory lookuputilizing a filename of the data, generating a new source name whenstoring data of the file a first time), dispersed storage error encodingthe segment allocation table to produce encoded table slices, andoutputting the encoded table slices to the DSN memory for storagetherein utilizing the segment allocation table vault source name. Themethod continues at step 360 where the processing module segments thedata in accordance with the segmentation scheme to produce a pluralityof data segments.

The method continues at step 362 where the processing module facilitatesstorage of the plurality of data segments in the DSN memory inaccordance with the information for storing the data. The facilitatingstorage of the plurality of data segments in the DSN memory includes foreach data segment of the plurality of data segments: dispersed storageerror encoding the data segment to produce a set of encoded data slices;generating a set of slice names corresponding to the encoded data slicesbased on a start segment vault source name of the segment allocationtable, wherein a common segment number of the set of slice namesincludes a sequentially increasing segment number (e.g., segmentsnumbers of the data are associated with segment numbers that continue toincrement by one); and sending the set of encoded data slices and theset of slice names to the DSN memory. Alternatively, or in addition to,the facilitating storage of the plurality of data segments in the DSNmemory further includes for each data segment of the plurality of datasegments: dispersed storage error encoding the data segment to produce aset of encoded data slices; generating a set of slice namescorresponding to the encoded data slices based on a start segment vaultsource name of the segment allocation table, wherein an append markerfield of the set of slice names includes a sequentially increasingappend marker (e.g., append marker starts at zero for a first datasection of a rally of data sections and sequentially increments by onefor each data section as data is appended); and sending the set ofencoded data slices and the set of slice names to the DSN memory.

FIG. 17B is a block diagram of a dispersed storage (DS) module thatoperates within one or more DS units to segment data in accordance withthe method described in FIG. 17A. The segmenting module 370 includes areceive data module 372, a generate segment allocation table (SAT)module 374, a store segment allocation table (SAT) module 376, a segmentdata module 378, and a store data segments module 380. The modules372-380 may be separate modules, may be sub-modules of another module,and/or a combination thereof.

The received data module 372 receives data 382 of a file for storage ina dispersed storage network (DSN) memory 22. The generate segmentallocation table module 374 determines a segmentation scheme 384 forstoring the data, determines how to store the data in accordance withthe segmentation scheme to produce information for storing the data 386,and generates an entry within a segment allocation table 388 associatedwith the file, wherein the entry includes the information for storingthe data 386 and the segmentation scheme 384. The generate segmentallocation table module 374 determines the segmentation scheme 384 basedon one or more of a previous segmentation scheme, a data size indicator,a data type indicator, a storage requirement, a vault identifier (ID), alookup, a message, and a query.

The store segment allocation table module 376 facilitates storage of thesegment allocation table 388 in the DSN memory 22. The store segmentallocation table module 376 facilitates storage of the segmentallocation table 388 by obtaining a segment allocation table vaultsource name, dispersed storage error encoding the segment allocationtable 388 to produce encoded table slices 390, and outputting theencoded table slices 390 to the DSN memory 22 for storage thereinutilizing the segment allocation table vault source name.

The segment data module 378 segments the data 382 in accordance with thesegmentation scheme 384 to produce a plurality of data segments 392. Thestore data segments module 380 facilitates storage of the plurality ofdata segments 392 in the DSN memory 22 in accordance with theinformation for storing the data 386. The store data segments module 380facilitates storage of the plurality of data segments 392 in the DSNmemory by for each data segment of the plurality of data segments 392:dispersed storage error encoding the data segment to produce a set ofencoded data slices of a plurality of sets of encoded data slices 394;generating a set of slice names 394 corresponding to the encoded dataslices based on a start segment vault source name of the segmentallocation table, wherein a common segment number of the set of slicenames includes a sequentially increasing segment number; and sending theset of encoded data slices and the set of slice names to the DSN memory22.

Alternatively, or in addition to, the store data segments module 380further facilitates storage of the plurality of data segments 392 in theDSN memory 22 by for each data segment of the plurality of data segments392: dispersed storage error encoding the data segment to produce theset of encoded data slices of the plurality of sets of encoded dataslices 394; generating the set of slice names corresponding to theencoded data slices based on a start segment vault source name of thesegment allocation table, wherein an append marker field of the set ofslice names includes a sequentially increasing append marker; andsending the set of encoded data slices and the set of slice names to theDSN memory 22.

FIG. 18 is a diagram illustrating an example of a directory filestructure. The directory file 400 includes a file name field 402, asnapshot field 404, a segmentation allocation table (SAT) vault sourcename field 406, a modification timestamp field 408, a size field 400and, a metadata field 412, and a content field 414. The file name field402 includes a filename entry to indicate one or more of a file name, afile identifier (ID), a file number, a block number, and a block numberrange. The snapshot field 404 includes a snapshot entry to indicate asnapshot name that may be associated with the file name. Multiplesnapshots may be associated with a common filename.

The SAT vault source name field 406 includes an entry to indicate eithera non-association of a snapshot with a filename (e.g., when the field iszero) or an association of a snapshot with a filename by indicating aSAT vault source name associated with SAT that contains accessinformation for the associated filename. For example, filename CS400.docis associated with snapshots foo and bar but not snapshot root and a SATvault source name is located at address BBB0 containing accessinformation for the snapshots foo and bar to the file CS400.doc.

The modification timestamp field 408 includes a modification timestampentry of a system timestamp value when the snapshot was created. Forexample, snapshot foo was created at timestamp t3 and snapshot bar wascreated at timestamp t6. The size field 410 includes a size entry toindicate a number of bytes of data of the file name. The metadata field412 includes metadata associated with the file name and snapshot. Themetadata may include one or more of directory metadata, a user ID, avault ID, a data object and, a filename, a data type indicator, and astorage requirement. The content field 414 includes content entry suchas a commonly accessed portion of the data associated with the filename. For example, the content field includes a reference table ofkeywords and locations in the filename CS400.doc.

FIG. 19 is a flowchart illustrating another example of updating adirectory. The method begins with step 416 where a processing module(e.g., a dispersed storage (DS) processing unit, DS module, etc.)receives new directory file information (e.g., from a new file entry,from a new snapshot entry). The new directory file information includesone or more of a filename, a snapshot identifier (ID), a segmentationallocation table (SAT) vault source name, a data size indicator,metadata of data, data, and data content. The method continues at step418 where the processing module determines a filename based on one ormore of receiving the filename with the new directory file information,a lookup based on a reference of the new directory file information, anda predetermination.

The method continues at step 420 where the processing module determinesan associated snapshot ID. The determination may be based on one or moreof a received snapshot ID, a current snapshot ID indicator, and asnapshot ID pointer. For example, the processing module determines thesnapshot ID to be foo when a current snapshot ID indicator indicatessnapshot foo. The method continues at step 422 where the processingmodule determines a SAT vault source name (e.g., a directory lookupbased on the filename).

The method continues at step 424 where the processing module determinesa modification timestamp based on a current timestamp of a system (e.g.,a real-time clock output). The method continues at step 426 where theprocessing module determines a size of data based on one or more ofreceiving a data size indicator and counting a number of bytes of data.The method continues at step 428 where the processing module determinesmetadata of the data based on one or more of received metadata of thedata and local directory metadata.

The method continues at step 430 where the processing module determinesa portion of the data as content. The determination may be based on oneor more of received data content, identifying the portion of data basedon a content pointer, a priority data indicator, summary data, and adata index. The method continues at step 432 where the processing modulecreates a directory file entry that includes one or more of thefilename, the snapshot ID, the SAT source name, the modificationtimestamp, the size, the metadata, and the content. Next, the processingmodule adds the directory file entry to a directory file. The processingmodule stores the directory file in a local memory and/or in a dispersedstorage network (DSN) memory as a plurality of sets of encoded directoryslices.

FIG. 20A is a diagram illustrating another example of a slice namestructure. The slice name 440 includes a slice index field 332 and avault source name field 442. The vault source name field 442 includes asource name field 336, an append marker field 444, and a segment numberfield 338. The append marker field 444 includes an append marker entrythat may be utilized to indicate whether an associated segment isincluded in a first region (e.g., as an original write operation) orwhether the associated segment is included in a region other than thefirst region (e.g., as an append operation). An append marker with avalue of zero indicates the first region. An append marker with a valueother than zero indicates a region other than the first region. Forexample, the append marker is assigned sequentially for each appendedregion (e.g., append marker 1 indicates region 2, append marker toindicates region 3, etc.). As another example, the append marker isassigned randomly when the append marker is nonzero. The segment numberfield 338 includes a segment number entry that corresponds to a segmentidentifier (ID) for each segment associated with storing data and/or asegment allocation table (SAT). For example, segment number zero isassociated with a SAT and segment number one is associated with a firstsegment of a contiguous number of segments associated with a firstregion of data.

The source name field 336 includes a vault ID field 340, a generationfield 342, and an object number field 344 (e.g., as previously discussedwith reference to FIG. 16A). As a specific example, a region 1 SAT isassigned a source name of AA, and append marker of 0, and a segmentnumber of 0 to produce a vault source name of AA00. An affiliated firstsegment of data that is associated with the same source name of AA isassigned an append marker of 0 and a segment number of 1 to produce avault source name of AA01. As another specific example, a region 2 SATis assigned a source name of AA when the second region is associatedwith the first region of source name AA, an append marker of 1 (e.g.,indicating region 2 which is a region other than the first region), anda segment number of 0 to produce a vault source name of AA10. Anaffiliated fifth segment of the data that is associated with the sourcename of AA is assigned the append marker of 1 and a segment number of 5to produce a vault source name of AA15.

FIG. 20B is a diagram illustrating another example of data segmentationthat includes a segment allocation table (SAT) 446 a plurality ofconsecutive segments 1-4 corresponding to initially storing data as afirst region. For example, the SAT 446 is stored in a dispersed storagenetwork (DSN) memory at a vault source name address of AA00. An appendmarker is set to zero for the first region. The SAT 446 includes a startsegment vault source name field 322 with an entry of AA01, a segmentsize field 324 with an entry of segment size of 100 bytes, asegmentation approach field 326 with an entry of a fixed segmentationapproach, and a total length field 328 entry of 340 bytes. Segments 1-4contains a maximum of 100 bytes in accordance with the segment size of100 bytes as indicated in the SAT 446. Segments 1-3 each contain 100bytes and segment 4 contains 40 bytes in accordance with the totallength of 340 bytes as indicated in the SAT. Note that segment 1 isstored in the DSN memory at a vault source name address of AA01 inaccordance with the start segment vault source name AA01 as indicated inthe SAT 446. Segments 2-4 are stored in the DSN memory at vault sourcename addresses of AA02-AA04 in accordance with contiguous segmentnumbering.

FIG. 20C is a diagram illustrating another example of data segmentationthat includes a segment allocation table (SAT) 448 a plurality ofconsecutive segments 5-8 corresponding to a second storing data as asecond region (e.g., data appended to a first region). For example, theSAT 448 is stored in a dispersed storage network (DSN) memory at a vaultsource name address of AA10. An append marker is set to a nonzero valueto indicate that the region is not a first region. The SAT 448 includestwo regions, wherein a first region includes a start segment vaultsource name entry of AA01, a segment size entry of 100 bytes, a fixedsegmentation approach, and a total length of 340 bytes.

The second region includes a start segment vault source name of AA15, asegment size of 300 bytes, a fixed segmentation approach, and a totallength of 1200 bytes. Segments 5-8 contains a maximum of 300 bytes inaccordance with the segment size of 300 bytes as indicated in the SAT.Segments 5-8 each contain 300 bytes in accordance with the total lengthof 1200 bytes as indicated in the SAT. Segment 5 is stored in the DSNmemory at a vault source name address of AA15 in accordance with thestart segment vault source name AA15 as indicated in the SAT. Thesegment number 5 is next sequentially after segment 4 of the firstregion as illustrated in FIG. 20B. Segments 5-8 are stored in the DSNmemory at vault source name addresses of AA15-AA18 in accordance withcontiguous segment numbering.

The append marker is set to a nonzero value indicating that the regionis not the first region. A SAT associated with region 1 (e.g., asdiscussed with reference to FIG. 20B) may be deleted when the SATassociated with region 2 is stored, wherein the SAT associated withregion 2 includes the region 1 information. Alternatively, the SATincludes information associated with region 2 and not with region 1.

FIG. 21 is a flowchart illustrating another example of segmenting data,which includes similar steps to FIG. 17A. The method begins with steps350-360 of FIG. 17A where a processing module (e.g., of a dispersedstorage (DS) processing unit) receives data of a file for storage in adispersed storage network (DSN) memory, determines a segmentation schemefor storing the data, determines how to store the data to produceinformation for storing the data, generates an entry within a segmentallocation table associated with the file, facilitates storage of thesegment allocation table in the DSN memory, and segments the data inaccordance with the segmentation scheme to produce a plurality of datasegments.

The method continues at step 450 where the processing module determinesan append marker for each vault source name of a plurality of vaultsource names corresponding to the plurality of data segments. Thedetermination may be based on one or more of a previous append markerincremented by one, a previous segmentation allocation table (SAT) vaultsource name, zero when no previous append marker exists, zero when thedata is associated with a first write scenario, a random number, areceived file name, and an append marker generation algorithm. Forexample, the processing module determines the append marker to be 5 whenthe previous append marker is 4. As another example, the processingmodule determines the append marker based on an output of a randomnumber generator such that the append marker is nonzero. As yet anotherexample, the processing module determines the append marker to be zerowhen the data for storage is a first write sequence (e.g., a firstregion). The method continues at step 362 of FIG. 17A where theprocessing module facilitates storage of the plurality of data segmentsin the DSN memory in accordance with the information for storing thedata and the plurality of append markers.

FIG. 22A is a flowchart illustrating an example of retrieving data. Themethod begins with step 452 where a processing module (e.g., a dispersedstorage (DS) processing module) receives a file retrieval request for afile, wherein the file includes one or more data regions, and wherein adata region of the one or more data regions is divided into a pluralityof data segments and stored as a plurality of sets of encoded dataslices in a dispersed storage network (DSN) memory. The file retrievalrequest may include one or more of a vault source name, a dataidentifier (ID), a segmentation allocation table (SAT) vault sourcename, a filename, a data region ID, and a retrieval requirement.

The method continues at step 454 were the processing model retrieves asegment allocation table (SAT) based on the file retrieval request,wherein the SAT includes a plurality of entries, and wherein an entry ofthe plurality of entries includes information regarding storing the dataregion in the DSN memory and a segmentation scheme regarding thedividing of the data region into the plurality of data segments. Forexample, the processing module retrieves a SAT vault source name from adirectory utilizing a filename of the file, generates SAT slice namesbased on the SAT slice names, sends a plurality of read requests to theDSN memory that includes the SAT slice names, receives SAT slices, anddecodes the SAT slices to reproduce the SAT.

The method continues at step 456 where the processing module identifiesthe plurality of sets of encoded data slices based on the segmentationscheme and the information regarding storing the data region. Theidentifying the plurality of sets of encoded data slices includesidentifying the plurality of data segments based on the segmentationscheme and identifying the plurality of sets of encoded data slicesbased on the plurality of data segments and the information regardingstoring the data region.

Alternatively, or in addition to, identifying the plurality of sets ofencoded data slices further includes extracting a start segment vaultsource name and a total length of the data region from the informationregarding storing the data region; extracting a segment size and asegmentation approach from the segmentation scheme; generating aplurality of segment vault source names for the plurality of datasegments based on the start segment vault source name, the total lengthof the data region, the segment size, and the segmentation approach(e.g., varying a segment number field of the plurality of segment vaultsource names for each segment, wherein a total number of segments isdetermined by dividing the total length by the segment size); andgenerating a plurality of sets of slices names for the plurality of setsof encoded data slices based on the plurality of segment vault sourcenames (e.g., varying a slice index field for each pillar).

The method continues at step 458 where the processing module retrievesat least a sufficient number of the plurality of sets of encoded dataslices to regenerate the data region. Such a sufficient number includesretrieving at least a decode threshold number of encoded data slices perset of the plurality of sets of encoded data slices. For example, theprocessing module facilitates sending a plurality of sets of readrequests to the DSN memory that includes the plurality of sets of slicenames, receives at least a decode threshold number of encoded dataslices per set of the plurality of sets of encoded data slices, decodeseach decode threshold number of encoded data slices per set of theplurality of sets of encoded data slices to reproduce a correspondingdata segment of the plurality of data segments, and aggregates theplurality of data segments to reproduce the data region.

Alternatively, or in addition to, the processing module identifies asecond entry of the segment allocation table corresponding to a seconddata region of the one or more data regions, wherein the second entryincludes second information regarding storing the second data region inthe DSN memory and a second segmentation scheme regarding the dividingof the second data region into a second plurality of data segments;identifies a second plurality of sets of encoded data slices based onthe second segmentation scheme and the second information regardingstoring the second data; and retrieves at least a sufficient number ofthe second plurality of sets of encoded data slices to regenerate thesecond data region.

Alternatively, or in addition to, the processing module receives thefile retrieval request, wherein the file includes a plurality of dataregions as the one or more data regions; identifies correspondingentries of the plurality of entries in the segment allocation table forthe plurality of data regions; identifies corresponding pluralities ofsets of encoded data slices based on corresponding segmentation schemesand corresponding information regarding storing the corresponding dataregion from the corresponding entries; and retrieves at least asufficient number of the corresponding pluralities of sets of encodeddata slices to regenerate the file.

FIG. 22B is a block diagram of a dispersed storage (DS) module withinone or more DS units operable to reproduce data in accordance with themethod described in FIG. 22A. The DS module 466 includes a requestretrieval module 468, a segment allocation table (SAT) retrieval module470, a slice identifying module 472, a slice retrieval module 474, andan entry identifying module 476. The module 468-476 may be separatemodules, sub-modules of another module, and/or a combination thereof.

The request retrieval module 468 facilitates receiving a file retrievalrequest 478 for a file (e.g., from a user device), wherein the fileincludes one or more data regions, and wherein a data region of the oneor more data regions is divided into a plurality of data segments andstored as a plurality of sets of encoded data slices in a dispersedstorage network (DSN) memory 22. Alternatively, or in addition to, therequest retrieval module 468 facilitates receiving the file retrievalrequest 478, wherein the file includes a plurality of data regions asthe one or more data regions.

The SAT retrieval module 470 facilitates retrieving a segment allocationtable (SAT) 482 based on the file retrieval request 478. The SATincludes a plurality of entries, and wherein an entry of the pluralityof entries includes information regarding storing the data region in theDSN memory 22 and a segmentation scheme regarding the dividing of thedata region into the plurality of data segments. For example, theretrieve segment allocation table 470 retrieves a SAT vault source namefrom a directory utilizing a filename of the file, generates SAT slicenames based on the SAT slice names, sends a plurality of read requeststo the DSN memory 22 that includes the SAT slice names, receives SATslices 480, and decodes the SAT slices 480 to reproduce the SAT 482.

The entry identifying module 476 identifies a second entry 484 of thesegment allocation table 482 corresponding to a second data region ofthe one or more data regions. The second entry includes secondinformation regarding storing the second data region in the DSN memoryand a second segmentation scheme regarding the dividing of the seconddata region into a second plurality of data segments. The entryidentifying module 476 further identifies corresponding entries 486 ofthe plurality of entries in the segment allocation table for theplurality of data regions when the request retrieval module 468facilitates receiving the file retrieval request, wherein the fileincludes the plurality of data regions as the one or more data regions.

The slice identifying module 472 identifies the plurality of sets ofencoded data slices as slice identifiers (IDs) 488 based on thesegmentation scheme and the information regarding storing the dataregion. The slice identifying module 472 further identifies a secondplurality of sets of encoded data slices as the slice IDs 488 based onthe second segmentation scheme and the second information of the secondentry 484 regarding storing the second data when the identify anotherentry module 476 identifies the second entry 484 of the segmentallocation table. The slice identifying module 472 also identifiescorresponding pluralities of sets of encoded data slices as the sliceIDs 488 based on corresponding segmentation schemes and correspondinginformation regarding storing the corresponding data region from thecorresponding entries 486 when the request retrieval module 468facilitates receiving the file retrieval request, wherein the fileincludes the plurality of data regions as the one or more data regions.

The slice identifying module 472 is further operable to identify theplurality of sets of encoded data slices by identifying the plurality ofdata segments based on the segmentation scheme and identifying theplurality of sets of encoded data slices based on the plurality of datasegments and the information regarding storing the data region.Alternatively, or in addition to, the slice identifying module 472further identifies the plurality of sets of encoded data slices byextracting a start segment vault source name and a total length of thedata region from the information regarding storing the data region;extracting a segment size and a segmentation approach from thesegmentation scheme; generating a plurality of segment vault sourcenames for the plurality of data segments based on the start segmentvault source name, the total length of the data region, the segmentsize, and the segmentation approach; and generating a plurality of setsof slices names for the plurality of sets of encoded data slices basedon the plurality of segment vault source names.

The slice retrieval module 474 facilitates retrieving at least asufficient number of the plurality of sets of encoded data slices 490 toregenerate the data region 492. The slice retrieval module 474 alsofacilitates retrieving at least a sufficient number of the secondplurality of sets of encoded data slices to regenerate the second dataregion when the identify another entry module 476 identifies the secondentry 484 of the segment allocation table 482. The slice retrievalmodule 474 further facilitates retrieving at least a sufficient numberof the corresponding pluralities of sets of encoded data slices toregenerate the file when the receive retrieval request module 468facilitates receiving the file retrieval request, wherein the fileincludes the plurality of data regions as the one or more data regions.

FIG. 22C is a flowchart illustrating another example of retrieving data,which include similar steps to FIG. 22A. The method begins with step 452of FIG. 22A where a processing module (e.g., of a dispersed storage (DS)processing unit, a DS module, etc.) receives a file retrieval requestfor a file, wherein the file includes one or more data regions, andwherein a data region of the one or more data regions is divided into aplurality of data segments and stored as a plurality of sets of encodeddata slices in a dispersed storage network (DSN) memory.

The method continues at step 500 where the processing module estimatesinformation regarding storing the data region in the DSN memory and asegmentation scheme regarding the dividing of the data region into theplurality of data segments to produce estimated information and anestimated segmentation scheme. For example, where the processing moduleestimates a first region start segment vault source name through an Nthsegment vault source name to produce N first region segment vault sourcenames. The determination may be based on a first region SAT vault sourcename (e.g., retrieved from a DSN directory lookup based on a filename ofthe request) and a most recent SAT vault source name (e.g., from therequest). For instance, the processing module estimates the first regionstart segment vault source name through the Nth segment vault sourcename as the first region SAT vault source name where an append marker isidentical and a segment number is varied from 1 to N. In addition, theprocessing module may produce vault source names for other regions toenable a broader prefetch. For example, the processing module sets theappend marker as a wildcard when establishing the vault source names.

The method continues at step 502 where the processing module retrievesat least some of the plurality of sets of encoded data slices based onthe estimated segmentation scheme and the estimated information. Theretrieving at least some of the plurality of sets of encoded data slicesincludes extracting a start segment vault source name and a total lengthof the data region from the estimated information; extracting a segmentsize and a segmentation approach from the estimated segmentation scheme;generating a plurality of segment vault source names for the pluralityof data segments based on the start segment vault source name, the totallength of the data region, the segment size, and the segmentationapproach; and generating a plurality of sets of slices names for the atleast some of the plurality of sets of encoded data slices based on theplurality of segment vault source names.

For example, the processing module sends a plurality of read requestsmessages to the DSN memory to recover a most recent SAT, a first regionSAT, and at most N first region segments in a common prefetch operation.The plurality of read requests messages may include the most recent SATvault source name, the first region SAT vault source name, and the Nfirst region segment vault source names. At least some of the firstregion segment vault source names may not exist (e.g., due to theestimation) and hence the DSN memory can't respond with correspondingencoded data slices. The number N may be set to an estimated number ofdata segments to acquire during a prefetch operation prior to recoveringan SAT with actual information with regards to a number of data segmentsassociated with a data region.

The method continues at step 504 where the processing module retrieves asegment allocation table (SAT) based on the file retrieval request,wherein the SAT includes a plurality of entries, and wherein an entry ofthe plurality of entries includes actual information regarding storingthe data region in the DSN memory and an actual segmentation schemeregarding the dividing of the data region into the plurality of datasegments. The method continues at step 506 where the processing modulecompares the estimated information and the estimated segmentation schemewith the actual information regarding storing the data region and theactual segmentation scheme. For example, the processing moduledetermines that there are more than N segments associated with the firstregion when the comparison indicates that an actual number of datasegments is greater than an estimated number of data segments. Asanother example, the processing module determines that there is morethan one data region (e.g., by extracting an entry associated withanother region from the SAT).

The method continues at step 508 where the processing module regeneratesthe data region from the at least some of the plurality of sets ofencoded data slices when the comparison is favorable. The method mayretrieve additional sets of encoded data slices when another data regionexists. When the comparison is unfavorable due to a lack of sets ofencoded data slices, the method continues at step 510 where theprocessing module retrieves additional sets of encoded data slices basedon a difference between the estimated information, the estimatedsegmentation scheme, the actual information regarding storing the dataregion, and the actual segmentation scheme. The method continues to step508. When the comparison is unfavorable due to an excess of sets ofencoded data slices, the method continues at step 512 where theprocessing module sends a cancellation message for the excess sets ofencoded data slices based on a difference between the estimatedinformation, the estimated segmentation scheme, the actual informationregarding storing the data region, and the actual segmentation scheme.The method continues to step 508.

The method continues to process more data regions when the one or moredata regions includes more than one data region. For example, for asecond data region of the one or more data regions, the processingmodule estimates second information regarding storing the second dataregion in the DSN memory and a second segmentation scheme regardingdividing of the second data region into a second plurality of datasegments to produce second estimated information and a second estimatedsegmentation scheme; retrieves at least some of a second plurality ofsets of encoded data slices based on the second estimated segmentationscheme and the second estimated information; accesses a second entry ofthe segment allocation table, wherein the second entry includes secondactual information regarding storing the second data region in the DSNmemory and a second actual segmentation scheme regarding the dividing ofthe second data region into the second plurality of data segments;compares the second estimated information and the second estimatedsegmentation scheme with the second actual information regarding storingthe data region and the second actual segmentation scheme; and when thecomparison is favorable, regenerating the second data region from the atleast some of the second plurality of sets of encoded data slices.

FIG. 22D is a block diagram of a DS module operable within one or moreDS units to reproduce data in accordance with the method described inFIG. 22C. The reproduce data module 520 includes a receive retrievalrequest module 522, an estimate module 524, a retrieve slices module526, a compare module 528, a regenerate module 530, and a cancellationmodule 532. The modules 522-532 may be separate modules, may besub-modules of another module, and/or a combination thereof.

The receive retrieval request module 522 facilitates receiving a fileretrieval request 534 for a file, wherein the file includes one or moredata regions, and wherein a data region of the one or more data regionsis divided into a plurality of data segments and stored as a pluralityof sets of encoded data slices in a dispersed storage network (DSN)memory 22. The estimating module 524 module estimates informationregarding storing the data region in the DSN memory and a segmentationscheme regarding the dividing of the data region into the plurality ofdata segments to produce estimated information and an estimatedsegmentation scheme as an estimated segmentation allocation table (SAT)536. The estimating module 524 module estimates second informationregarding storing the second data region in the DSN memory 22 and asecond segmentation scheme regarding dividing of the second data regioninto a second plurality of data segments to produce second estimatedinformation and a second estimated segmentation scheme when retrieving asecond data region of the one or more data regions.

The retrieve slices module 526 facilities retrieving at least some ofthe plurality of sets of encoded data slices 538 based on the estimatedsegmentation scheme and the estimated information of the estimated SAT536 and facilitates retrieving an actual segment allocation table (SAT)542 based on the file retrieval request 522 (e.g., by retrieving SATslices 540), wherein the actual SAT 542 includes a plurality of entries,and wherein an entry of the plurality of entries includes actualinformation regarding storing the data region in the DSN memory 22 andan actual segmentation scheme regarding the dividing of the data regioninto the plurality of data segments. The retrieve slices module 526facilitates retrieving at least some of a second plurality of sets ofencoded data slices based on the second estimated segmentation schemeand the second estimated information and accessing a second entry of thesegment allocation table, wherein the second entry includes secondactual information regarding storing the second data region in the DSNmemory 22 and a second actual segmentation scheme regarding the dividingof the second data region into the second plurality of data segmentswhen retrieving a for second data region of the one or more dataregions.

The retrieve slices module 526 retrieves at least some of the pluralityof sets of encoded data slices 538 by extracting a start segment vaultsource name and a total length of the data region from the estimatedinformation; extracting a segment size and a segmentation approach fromthe estimated segmentation scheme; generating a plurality of segmentvault source names for the plurality of data segments based on the startsegment vault source name, the total length of the data region, thesegment size, and the segmentation approach; generating a plurality ofsets of slices names 537 for the at least some of the plurality of setsof encoded data slices based on the plurality of segment vault sourcenames; and sending a plurality of sets of encoded data slice requests tothe DSN memory 22 that includes the plurality of sets of slice names537.

The compare module 528 compares the estimated information and theestimated segmentation scheme of the estimated SAT 536 with the actualinformation regarding storing the data region and the actualsegmentation scheme of the actual SAT 542. The compare module 528compares the second estimated information and the second estimatedsegmentation scheme with the second actual information regarding storingthe data region and the second actual segmentation scheme whenretrieving a for second data region of the one or more data regions. Forexample, the compare module 528 outputs additional slices identifiers(IDs) 544 corresponding to remaining encoded data slices for retrievalwhen an unfavorable comparison indicates that there are more actual datasegments than estimated. As another example, the compare module 528outputs excess slice IDs 546 corresponding to excess slice names forretrieval cancellations when an unfavorable comparison indicates thatthere are fewer actual data segments than estimated.

The regenerate module 530 regenerates data 548 of the data region fromthe at least some of the plurality of sets of encoded data slices 540when the comparison is favorable. The regenerate module 530 regeneratesthe second data region from the at least some of the second plurality ofsets of encoded data slices when the comparison is favorable whenretrieving a for second data region of the one or more data regions. Theretrieve slices module 526 facilitates retrieving additional sets ofencoded data slices utilizing the additional slices IDs 544 based on adifference between the estimated information, the estimated segmentationscheme, the actual information regarding storing the data region, andthe actual segmentation scheme when a comparison is unfavorable due to alack of sets of encoded data slices. Next, the regenerate module 530regenerates the data 548 of the data region from the additional sets ofencoded data slices.

The cancellation module 500 sends a cancellation message 550 to the DSNmemory 22 for excess sets of encoded data slices based on a differencebetween the estimated information, the estimated segmentation scheme,the actual information regarding storing the data region, and the actualsegmentation scheme when the comparison is unfavorable due to an excessof sets of encoded data slices. The DSN memory 22 may cancel sending anyfurther encoded data slices associated with the data 548 to the retrieveslices module 526. Next, the regenerate module 530 regenerates the data548 of the data region from the at least some of the plurality of setsof encoded data slices 540.

FIG. 23 is a flowchart illustrating another example of storing data,which includes similar steps to FIGS. 13 and 14A. The method begins withstep 242 of FIG. 13 where a processing module (e.g., of a dispersedstorage (DS) processing unit) receives data for storage. The methodcontinues at step 560 where the processing module dispersed storageerror encodes the data to produce a plurality of sets of encode dataslices utilizing a first set of error coding dispersal storage functionparameters. The processing module may generate the first set of errorcoding dispersal storage function parameters based on storagerequirements of the data. For example, the processing module generatesthe first set of error coding dispersal storage function parameters toinclude a relatively large difference between a pillar width number anda decode threshold number when storage requirements indicate a highlevel of reliability is required.

The method continues at step 562 where the processing module selects afirst set of dispersed storage (DS) units based on the data. Forexample, the processing module selects the first set of DS units tomatch storage requirements and in accordance with the first set of errorcoding dispersal storage function parameters. For example, theprocessing module selects DS units 1-16 when DS units 1-16 areassociated with favorable estimated reliability when the first set oferror coding dispersal storage function parameters include a pillarwidth of 16 and a decode threshold of 10. The method continues at step564 where the processing module sends the plurality of sets of encodedata slices to the first set of DS units for storage therein. Forexample, the processing module sends a plurality of sets of writerequest messages to the first set of DS units that includes theplurality of sets of encoded data slices.

The method continues with step 266 of FIG. 14A where the processingmodule updates directory metadata based on the data. The methodcontinues at step 566 where the processing module dispersed storageerror encodes the directory metadata to produce a plurality of sets ofencoded directory slices based on a second set of error coding dispersalstorage function parameters. The processing module may generate thesecond set of error coding dispersal storage function parameters basedon one or more of storage requirements of the data, the first set oferror coding dispersal storage function parameters, the data, thedirectory metadata, storage requirements of the directory metadata, anda data type indicator. For example, the processing module generates thesecond set of error coding dispersal storage function parameters toinclude a relatively small pillar width and decode threshold number whenthe directory metadata storage requirements indicate a low accesslatency requirement.

The method continues at step 568 where the processing module selects asecond set of DS units based on the directory metadata. For example, theprocessing module selects the second set of DS units to match directorymetadata storage requirements and in accordance with the second set oferror coding dispersal storage function parameters. For example, theprocessing module selects DS units 20-23 when DS units 20-23 areassociated with favorable estimated access latency and when the seconderror coding dispersal storage function parameters include a pillarwidth of 4 and a decode threshold of 3. The method continues at step 570where the processing module sends the plurality of sets of encodeddirectory slices to the second set of DS units for storage therein. Forexample, the processing module sends a plurality of sets of writerequest messages to the second set of DS units that includes theplurality of sets of encoded directory slices.

As may be used herein, the terms “substantially” and “approximately”provides an industry-accepted tolerance for its corresponding termand/or relativity between items. Such an industry-accepted toleranceranges from less than one percent to fifty percent and corresponds to,but is not limited to, component values, integrated circuit processvariations, temperature variations, rise and fall times, and/or thermalnoise. Such relativity between items ranges from a difference of a fewpercent to magnitude differences. As may also be used herein, theterm(s) “operably coupled to”, “coupled to”, and/or “coupling” includesdirect coupling between items and/or indirect coupling between items viaan intervening item (e.g., an item includes, but is not limited to, acomponent, an element, a circuit, and/or a module) where, for indirectcoupling, the intervening item does not modify the information of asignal but may adjust its current level, voltage level, and/or powerlevel. As may further be used herein, inferred coupling (i.e., where oneelement is coupled to another element by inference) includes direct andindirect coupling between two items in the same manner as “coupled to”.As may even further be used herein, the term “operable to” or “operablycoupled to” indicates that an item includes one or more of powerconnections, input(s), output(s), etc., to perform, when activated, oneor more its corresponding functions and may further include inferredcoupling to one or more other items. As may still further be usedherein, the term “associated with”, includes direct and/or indirectcoupling of separate items and/or one item being embedded within anotheritem. As may be used herein, the term “compares favorably”, indicatesthat a comparison between two or more items, signals, etc., provides adesired relationship. For example, when the desired relationship is thatsignal 1 has a greater magnitude than signal 2, a favorable comparisonmay be achieved when the magnitude of signal 1 is greater than that ofsignal 2 or when the magnitude of signal 2 is less than that of signal1.

As may also be used herein, the terms “processing module”, “processingcircuit”, and/or “processing unit” may be a single processing device ora plurality of processing devices. Such a processing device may be amicroprocessor, micro-controller, digital signal processor,microcomputer, central processing unit, field programmable gate array,programmable logic device, state machine, logic circuitry, analogcircuitry, digital circuitry, and/or any device that manipulates signals(analog and/or digital) based on hard coding of the circuitry and/oroperational instructions. The processing module, module, processingcircuit, and/or processing unit may be, or further include, memoryand/or an integrated memory element, which may be a single memorydevice, a plurality of memory devices, and/or embedded circuitry ofanother processing module, module, processing circuit, and/or processingunit. Such a memory device may be a read-only memory, random accessmemory, volatile memory, non-volatile memory, static memory, dynamicmemory, flash memory, cache memory, and/or any device that storesdigital information. Note that if the processing module, module,processing circuit, and/or processing unit includes more than oneprocessing device, the processing devices may be centrally located(e.g., directly coupled together via a wired and/or wireless busstructure) or may be distributedly located (e.g., cloud computing viaindirect coupling via a local area network and/or a wide area network).Further note that if the processing module, module, processing circuit,and/or processing unit implements one or more of its functions via astate machine, analog circuitry, digital circuitry, and/or logiccircuitry, the memory and/or memory element storing the correspondingoperational instructions may be embedded within, or external to, thecircuitry comprising the state machine, analog circuitry, digitalcircuitry, and/or logic circuitry. Still further note that, the memoryelement may store, and the processing module, module, processingcircuit, and/or processing unit executes, hard coded and/or operationalinstructions corresponding to at least some of the steps and/orfunctions illustrated in one or more of the Figures. Such a memorydevice or memory element can be included in an article of manufacture.

The present invention has been described above with the aid of methodsteps illustrating the performance of specified functions andrelationships thereof. The boundaries and sequence of these functionalbuilding blocks and method steps have been arbitrarily defined hereinfor convenience of description. Alternate boundaries and sequences canbe defined so long as the specified functions and relationships areappropriately performed. Any such alternate boundaries or sequences arethus within the scope and spirit of the claimed invention. Further, theboundaries of these functional building blocks have been arbitrarilydefined for convenience of description. Alternate boundaries could bedefined as long as the certain significant functions are appropriatelyperformed. Similarly, flow diagram blocks may also have been arbitrarilydefined herein to illustrate certain significant functionality. To theextent used, the flow diagram block boundaries and sequence could havebeen defined otherwise and still perform the certain significantfunctionality. Such alternate definitions of both functional buildingblocks and flow diagram blocks and sequences are thus within the scopeand spirit of the claimed invention. One of average skill in the artwill also recognize that the functional building blocks, and otherillustrative blocks, modules and components herein, can be implementedas illustrated or by discrete components, application specificintegrated circuits, processors executing appropriate software and thelike or any combination thereof.

The present invention may have also been described, at least in part, interms of one or more embodiments. An embodiment of the present inventionis used herein to illustrate the present invention, an aspect thereof, afeature thereof, a concept thereof, and/or an example thereof. Aphysical embodiment of an apparatus, an article of manufacture, amachine, and/or of a process that embodies the present invention mayinclude one or more of the aspects, features, concepts, examples, etc.described with reference to one or more of the embodiments discussedherein. Further, from figure to figure, the embodiments may incorporatethe same or similarly named functions, steps, modules, etc. that may usethe same or different reference numbers and, as such, the functions,steps, modules, etc. may be the same or similar functions, steps,modules, etc. or different ones.

While the transistors in the above described figure(s) is/are shown asfield effect transistors (FETs), as one of ordinary skill in the artwill appreciate, the transistors may be implemented using any type oftransistor structure including, but not limited to, bipolar, metal oxidesemiconductor field effect transistors (MOSFET), N-well transistors,P-well transistors, enhancement mode, depletion mode, and zero voltagethreshold (VT) transistors.

Unless specifically stated to the contra, signals to, from, and/orbetween elements in a figure of any of the figures presented herein maybe analog or digital, continuous time or discrete time, and single-endedor differential. For instance, if a signal path is shown as asingle-ended path, it also represents a differential signal path.Similarly, if a signal path is shown as a differential path, it alsorepresents a single-ended signal path. While one or more particulararchitectures are described herein, other architectures can likewise beimplemented that use one or more data buses not expressly shown, directconnectivity between elements, and/or indirect coupling between otherelements as recognized by one of average skill in the art.

The term “module” is used in the description of the various embodimentsof the present invention. A module includes a processing module, afunctional block, hardware, and/or software stored on memory forperforming one or more functions as may be described herein. Note that,if the module is implemented via hardware, the hardware may operateindependently and/or in conjunction software and/or firmware. As usedherein, a module may contain one or more sub-modules, each of which maybe one or more modules.

While particular combinations of various functions and features of thepresent invention have been expressly described herein, othercombinations of these features and functions are likewise possible. Thepresent invention is not limited by the particular examples disclosedherein and expressly incorporates these other combinations.

What is claimed is:
 1. A method for updating directory information in adistributed storage network (DSN) memory, comprises: dispersed storageerror encoding data to produce a plurality of sets of encoded dataslices; transmitting the plurality of sets of encoded data slices to theDSN memory for storing the plurality of sets of encoded data slices;determining to update directory metadata stored in a local cache memoryin response to storing the plurality of sets of encoded data slices inthe DSN memory; updating the directory metadata stored in the localcache memory; determining to synchronize the directory metadata storedin the local cache memory with directory information stored in the DSNmemory; in response to determining to synchronize the directorymetadata, dispersed storage error encoding the directory metadata toproduce a plurality of sets of encoded directory metadata slices; andtransmitting the plurality of sets of encoded directory metadata slicesto the DSN memory for storing the plurality of sets of encoded directorymetadata slices with the directory information stored in the DSN memory.2. The method of claim 1, wherein transmitting the plurality of sets ofencoded data slices to the DSN memory for storing the plurality of setsof encoded data slices includes: transmitting one or more data slicewrite requests to the DSN memory for storing the plurality of sets ofencoded data slices in the DSN memory, wherein the one or more dataslice write requests includes a first transaction number.
 3. The methodof claim 2, wherein transmitting the plurality of sets of encodeddirectory metadata slices to the DSN memory for storing the plurality ofsets of encoded directory metadata slices includes: selecting a portionof the directory metadata to produce the plurality of sets of encodeddirectory metadata slices, wherein the portion of the directory metadatais selected based on a change indicator indicating a last update to thedirectory information in the DSN memory; and transmitting one or moredirectory metadata write requests to the DSN memory for storing theplurality of sets of encoded directory metadata slices in the DSNmemory, wherein the one or more directory metadata write requestsincludes a second transaction number.
 4. The method of claim 3, whereinthe one or more directory metadata write requests further includes arevision number corresponding to the portion of the directory metadatabeing stored and an expected slice revision number corresponding to alast revision number of the directory metadata stored in the local cachememory.
 5. The method of claim 4, further comprising: when a favorablewrite response condition exists for the one or more data slice writerequests and the one or more directory metadata write requests,transmitting one or more common commit requests to the DSN memory tocommit storage of the plurality of sets of encoded data slices and theplurality of sets of encoded directory metadata slices, wherein the oneor more common commit requests includes the first transaction number andthe second transaction number.
 6. The method of claim 1, whereinupdating directory metadata stored in the local cache memory to produceupdated directory metadata comprises: retrieving the directory metadatafrom at least one of the DSN memory and a local memory; determining aDSN memory storage location information for the plurality of sets ofencoded data slices, wherein the DSN memory storage location informationincludes one or more of: a source name corresponding to a DSN memorystorage location, a data size indicator, a data type indicator, snapshotinformation, a timestamp; and a segment allocation table; and modifyingthe directory metadata to include a filename associated with the dataand the DSN memory storage location to produce the updated directorymetadata.
 7. The method of claim 1, wherein determining to synchronizethe directory metadata stored in the local cache memory with directoryinformation stored in the DSN memory is based on one or more of thefollowing: a time interval between a last update and a time threshold;an indicator requiring synchronization after a store operation; a datatype indicator; a frequency of change indicator; a system activityindicator; a timestamp of a previous synchronization message; or acommand.
 8. A dispersed storage (DS) device, comprises: at least onelocal memory, wherein the local memory stores directory metadata; andone or more processing modules that include at least one processingdevice, operable to: retrieve directory metadata from the local memoryand directory information from a dispersed storage network (DSN) memory;determine directory metadata updates to the directory metadata in thelocal memory based on the directory information from the DSN memory;update the directory metadata in the local memory using the directorymetadata updates; determine to synchronize the directory metadata in thelocal memory with the directory information in the DSN memory; dispersedstorage error encode a portion of the directory metadata to produce aplurality of sets of encoded directory metadata slices; and transmit theplurality of sets of encoded directory metadata slices to the DSN memoryfor storing the plurality of sets of encoded directory metadata sliceswith the directory information stored in the DSN memory.
 9. The DSdevice of claim 8, wherein the one or more processing modules areoperable to: determine synchronization status information; and determineto synchronize the directory metadata in the local memory with thedirectory information in the DSN memory based on the synchronizationstatus information.
 10. The DS device of claim 9, wherein thesynchronization status information is based on at least one of: a timer;a number of previous failed synchronization attempts; time elapsed sincea last attempt to synchronize; one or more historical synchronizationattempts; an update frequency indicator; a number of users authorized toaccess a common stored vault; or a service level agreement.
 11. The DSdevice of claim 8, wherein the one or more processing modules areoperable to select a portion of the directory metadata to produce theplurality of sets of encoded directory metadata slices based on a changeindicator indicating a last update to the directory information in theDSN memory.
 12. The DS device of claim 8, wherein the one or moreprocessing modules are operable to transmit the plurality of sets ofencoded directory metadata slices to the DSN memory for storing theplurality of sets of encoded directory metadata slices with thedirectory information stored in the DSN memory by: transmitting one ormore directory metadata write requests to the DSN memory for storing theplurality of sets of encoded directory metadata slices in the DSNmemory, wherein the one or more directory metadata write requestsincludes a transaction number.
 13. The DS device of claim 12, whereinthe one or more directory metadata write requests further include arevision number corresponding to the portion of the directory metadatabeing stored and an expected slice revision number corresponding to alast revision number of the directory metadata stored in the localmemory.
 14. A dispersed storage (DS) device, comprises: at least onememory; one or more processing modules that include at least oneprocessing device, operable to: receive an add snapshot request, whereinthe add snapshot request includes information to identify a childsnapshot, an associated parent snapshot and a snapshot file; retrieve aplurality of encoded snapshot file slices from dispersed a storagenetwork (DSN) memory; dispersed storage error decode the plurality ofencoded snapshot file slices to recover the snapshot file, wherein thesnapshot file indicates files authorized for access; and modify thesnapshot file to associate the child snapshot with the associated parentsnapshot and create a timestamp indicating a time of modification. 15.The DS device of claim 14, wherein the one or more processing modulesare further operable to: recover a parent snapshot directory fileassociated with the parent snapshot from the DSN memory, wherein theparent snapshot directory file includes a plurality of parent filenames; create a child snapshot directory file associated with the childsnapshot to include the plurality of parent file names included in theparent snapshot directory file at the time of modification indicated bythe timestamp; dispersed error encode the child snapshot directory fileto produce a plurality of sets of encoded child snapshot directory fileslices; and transmit the plurality of sets of child snapshot directoryfile slices to the DSN memory for storing in the DSN memory.
 16. The DSdevice of claim 15, wherein the one or more processing modules arefurther operable to: receive an add directory entry request, wherein theadd directory entry request includes information to identify the childsnapshot directory file and a new file name; recover the child snapshotdirectory file from the DSN memory; modify the child snapshot directoryfile to include the new file name; disperse error encode the modifiedchild snapshot directory file to produce a plurality of sets of encodedmodified child snapshot directory file slices; and transmit theplurality of sets of modified child snapshot directory file slices tothe DSN memory for storing in the DSN memory.
 17. The DS device of claim16, wherein the one or more processing modules do not update the parentsnapshot directory file with the new file name included in the childsnapshot directory file.
 18. The DS device of claim 15, wherein the oneor more processing modules are further operable to: receive a deletedirectory entry request, wherein the delete directory entry requestincludes information to identify the child snapshot directory file and acurrent file name for deletion; recover the child snapshot directoryfile from the DSN memory; modify the child snapshot directory file todisassociate the current file name for deletion from the child snapshotdirectory file; disperse error encoding the modified child snapshotdirectory file to produce a plurality of sets of modified encoded childsnapshot directory file slices; and transmit the plurality of sets ofmodified child snapshot directory file slices to the DSN memory forstoring in the DSN memory.
 19. The DS device of claim 18, wherein thecurrent file name for deletion from the child snapshot directory file isincluded in the plurality of parent file names and wherein the currentfile name from deletion remains in the parent snapshot directory fileafter deletion from the child snapshot directory file.